In my review of my Droid Turbo, I mentioned in passing that I was frustrated by how slippery a lot of cell phones were. I was in the Verizon store the other day killing time while they fixed something on my kids' phone, so I tried holding a bunch.
The slipperiest by far were the HTC One M8 and the LG G3. Both, probably not coincidentally, get high marks for being attractive due to their metal or faux metal backs, but the same backs make them like a wet bar of soap to hold. You can put a no slip case on them of course, but then if you are going to put them in a case, why buy a phone that is promoted in large part on its looks?
My Droid Turbo is OK, with no slip surface around the edges but a very slick back, at least the nylon back one I have.
The Galaxy S5 is better than average. Its back gets a lot of grief for being ugly, but it will not slide around in the hand and is comfortable to hold.
Until this week, the no-slip champion for me was the Moto X with the bamboo case (it is real wood veneer, not some plastic fake thing). It looks good to my eye and it is very grippy in the hand.
But there is a new champion. I tried the Moto X with the new football leather backing (again, real football leather). This thing is not going to slide out of your hand (unless maybe if you are Jay Cutler). The looks are ... different, but I could get used to it. Phones for me are a convenience item, not a fashion item. The Moto X's only problems are a small battery and a camera that is a bit weak. Which is why I bought the Droid Turbo, which is a very similar phone but with a bigger battery. Just wish they had all the cool Moto Maker options the Moto X has.