Best smartphone of 2015 so far: iPhone 6 vs Samsung Galaxy S6 vs HTC One M9 vs LG G4

With the LG G4 recently going on sale, the class of 2015 can finally assemble. The iPhone 6, Samsung Galaxy S6, LG G4 and HTC One M9 are the best smartphones of the year - but which is best?

Apple remains a force to be reckoned with, thanks to the iPhone 6 and 6 Plus. But where arch rival Samsung had slipped up with the Galaxy S4 and S5, it came out fighting in 2015 with the Galaxy S6 and S6 edge, a one-two move bringing it right back into the fight.

On the contrary, a hugely impressive performance in 2013 and 2014 gave HTC the number one spot on the Android podium, but a lack of innovation for the new One M9 puts it under pressure. Meanwhile, LG turned heads with the leather-clad G4 and its excellent camera, but last year's software criticisms remain. All four are strong contenders for the title of Best Phone of 2015, but which is best? And is there even a clear winner?

Time to find out.

iPhone 6 vs Galaxy S6 vs One M9 vs LG G4: Design and Ergonomics

Samsung must surely win the award for most improved in 2015. The Galaxy S6 and S edge are every bit the iPhone rival we've demanded from Samsung for the past three years. We've not included the edge here because of its massive price (£100 more than the regular S6), but even the normal model has a sense of value and craftsmanship not seen before from Samsung's flagships. The aluminium chassis is very similar to the iPhone 6, but I'd rather Samsung borrowed good design rather than come up with something inferior of its own.

Also, the sharper edges and glass back provide slightly more grip than the eel-like iPhone, which is always a good thing. Speaking of grip, the iPhone is probably feels the least secure of the bunch. The plastic LG and Nexus 6 (we weren't sent a leather G4) feel equally safe, while the HTC's aluminium body is sharper and grippier than the iPhone.

To my eyes, there is very little to choose between the iPhone, Galaxy S6 and One M9. They are glass and aluminium, they have shiny chamfered edges and they all feel like they're worth their substantial price tags. Sadly, this can't be said for the plastic version of the LG G4. At £490, it's a fair bit cheaper than the £539 iPhone and £569 Samsung, but then it feels like it.

The faux metal looks better in LG's promotional materials than in reality, where it is most definitely shiny plastic.Having said that, I'm a fan of the slight curve to the screen and the tiny bezels around its edge. LG also lose points for the rear-mounted buttons. They look good, but are difficult to press accurately - especially the screen lock button.

Also struggling with button placement is the One M9, which doesn't do enough to differentiate its screen lock and volume buttons; I kept getting them mixed up without looking, and so will you.

iPhone 6 vs Galaxy S6 vs One M9 vs LG G4: Screen

The growth rate of smartphone screens has finally - some would say mercifully - slowed in 2015. The LG (5.5in), HTC (5in) and Samsung (5.1in) all remain unchanged from last year's models. Only the iPhone has seen an increase, up from 4in in 2013/14 to 4.6in for 2014/15 - and don't forget the 5.5in iPhone 6 Plus.

HTC has also stuck with the same Full HD 1920 x 1080 resolution as the One M7 and M8, while LG has kept the same 2560 x 1440 resolution for the G4, carried over from the G3. This is a resolution now shared by the Galaxy S6, up from Full HD, while the iPhone 6 is 750 x 1334 - fairly middling in this flagship company, but pixel count isn't everything.

Lined up side by side with brightness cranked up to 100% and showing the same web page, you can see the following:

• The HTC is the least bright
• The iPhone has the warmest colour, making white look slightly pink
• The LG is the coolest, with whites looking slightly blue
• It's almost impossible to spot the extra pixels of the Samsung and LG

Viewed in isolation, you'd have a real tough time telling the four phones apart, but when looking at them all together subtle difference become more apparent. The LG is probably the most accurate, but a side effect is it lack the visual punch of the iPhone and Samsung. Meanwhile, the HTC struggles to stand out. The winner probably lies somewhere between the Galaxy S6 and the iPhone; I'd like a phone with their combined brightness and punch, but with a temperature which is warmer than the Samsung but cooler than the iPhone.

iPhone 6 vs Galaxy S6 vs One M9 vs LG G4: Camera

It's long been said that the iPhone's camera is the best because it's the easiest to use and the most reliable, but now things aren't quite so simple because the Galaxy S6's camera is utterly superb. It is head and shoulders above the iPhone 6, while the LG G4 also takes superior snaps.

Photos taken with the G4 (and especially the S6) have a extra level of quality and realism to them which isn't found with the iPhone; colours are rich without being overly saturated, scenes are bright without being over-exposed, and the results are hugely impressive. The iPhone is still a very good camera, but the Android competition has taken the game onto a new level this year; the iPhone 6s will need a big update to reclaim the top step.

Meanwhile, HTC's decision to install a 20-megapixel sensor instead of the M8's 4MP 'Ultrapixel' sensor hasn't paid off. It may have more pixels than the iPhone, G4 and S6 (8MP, 16MP and 16MP respectively), but the HTC's camera is disappointing. There's a real lack of detail, and although colour reproduction is good, the results just can't touch those of the other three.

My only complaint with the Samsung is how it occasionally failed to refocus when the subject moved quickly from near to far, but a tap of the screen to focus fixes this.

iPhone 6 vs Galaxy S6 vs One M9 vs LG G4: Software and Performance

Performance is so similar between top-end smartphones these days that trying to tell them apart is largely a waste of your time. They all open apps pretty much instantly, they all play HD video smoothly, they all play demanding 3D games without difficulty (although heat is a universal side effect here) and they never really feel lacking in any noticeable way.

You can argue until you're blue in the face about whether one octa-core processor is better than the other, and if the iPhone's lack of RAM is a problem, but ultimately there is nothing to split them.

However, with software it's a different story. The LG, Samsung and HTC all run Android 5 Lollipop, but they go about it in three very different ways. LG's is a slightly garish affair, with bright colours and a design which feels playful but perhaps more childish than most consumers will be comfortable with. An innovative feature of the G4 is Knock Code, where tapping a pattern into the screen both awakens and unlocks the phone.

HTC has stuck with its tried and tested formula of adding the Blinkfeed page to the left of the home screen; this is a place for news and social media highlights.

Samsung has learnt some serious lessons from the Galaxy S4 and S5, as where they had more features and settings than you can shake a selfie stick at, the S6 is a far simpler and refined experience. It's still oozing with features, but many are hidden out of the way and where they're less likely to confuse.

As for the iPhone, iOS is the most refined it's ever been and offers an excellent blend of simplicity and power that makes it difficult to criticise. Saying that, the home screen interface with its grid of app icons and folders is starting to feel old.

The lack of widgets and customisation levels to match Android (without jailbreaking) are the same iOS bugbears they've always been, and there will always be those who prefer Android's openness over Apple's walled-garden approach.

But picking positives and negatives is more difficult than ever.

iPhone 6 vs Galaxy S6 vs One M9 vs LG G4: The Verdict

This is the tough bit. Where the iPhone and HTC have cleaned up in previous years by offering superior design, Samsung has put in its strongest performance yet with the Galaxy S6. Its design is infinitely better than previous generations; the screen is superb; the software has finally learnt that less is more, and the camera is truly best-in-class.

The lack of waterproofing, removable battery and expandable storage is a shame, but never having these features hasn't done the iPhone much harm. The LG is let down by a cheap-feeling plastic body (unless you pay a premium for leather) and a specification sheet which has barely changed since last year. The HTC also offers little reason to upgrade on the year-old One M8, while that rear camera is a real letdown when tested alongside the Samsung.

Apple finally responded to consumer desire for larger screens with the iPhone 6, but the equally potent calls for a phone less prone to smashing was ignored by the handset's extremely slippery body, meaning a bulky base or cover is more necessity than luxury. Another design shortfall, although attractive, is the glass back of the Galaxy S6; who knows how many drops that will shrug off before shattering, when a plastic S5 would carry on unscathed.

To draw a definitive conclusion here is nigh-on impossible. For me, it's a straight fight between the iPhone and the Galaxy S6, and the winner should come down to which software and ecosystem you prefer; iOS vs Android, Google vs Apple. Now Samsung has got itself back in the race, consumers have never had it so good. And one thing's for sure - the iPhone 6s will need one hell of a camera to stay in the race.