It's all in the design really. I had a Droid x which is a 4.3 inch screen, I got a thunderbolt today which is the same size screen. I noticed the difference immediately when I put it in my front pocket.

The Droid was tall where the thunderbolt feels wider, the bolt feels heavier in the hand but it feels better holding it. The HTC size is perfect, I feel they can go up to 4.5 inch screen in this same package which would work great.