I had a chance to spend some time with both of the new Galaxy S6 models today and my first thoughts were that it's a totally underwhelming device.
The standard S6 looks, from the front at least, like an S5. When you pick it up it has the cold hard feel of an Apple or HTC product, but the design doesn't flow as well as either of the competitors. In fact up against the HTC One M9 or Sony Xperia Z3 I find very little that's appealing about Samsung's new design language.
When turned on the S6 is little better. Side by side with the HTC or Sony you can barely tell that there are twice as many pixels on screen. The display is very nice, but alongside the S5 it doesn't represent a massive step forward.
This change in design has cost two of my favourite Samsung features - the replaceable battery and the memory card slot. Dual wireless charging circuits don't feel like a huge compensation. In use the S6 feels just like the S5, there's been no magic pill that suddenly makes TouchWiz work any differently. It is what it is. If you can't live with TouchWiz this isn't the phone for you. If you've previously owned an S5 you'll have no problems adapting.
The S6 Edge is a completely different kettle of fish. For some reason the screen here looks a million times better than the standard phone. The image looks like it's painted onto the glass, whilst the curves of the screen edges are aesthetically very pleasing. Functional? Not in the slightest, but I don't believe that's why they're there.
Of the two phones, one clearly has a reason for existing. The S6 Edge is a beautiful piece of kit, it's screen and curves more than justifying the compromises that Samsung made to get it here. It is a joy to hold and use. The S6 however feels like something Samsung whipped up when it realised that its new screen technology wasn't going to yield enough units to maintain its sales numbers. It may as well have stuffed the new innards into an S5 and offered that instead. At least customers would have had the choice of function against form.
For Android customers the S6 Edge is the phone to have. If it is in stock and you can afford the premium that Samsung is asking then this is without question the Android phone to buy. If you can't run to the Edge then the S6 is a poor substitute. I'd recommend the Xperia Z3 as the better phone, at least you will have a card slot and waterproofing even if you don't have the beautiful curved screen.
If you must stay with Samsung then the Note 4 is probably a better choice than the S6, a bigger screen and replaceable battery and a card slot all weigh in its favour.