If I had to venture a guess: the native kickstand? Hey, once you go native kickstand, it's hard to go back/give up!

Considering it's something I use all the time, it's what has always kept me from seriously considering the Rezound (don't like kickstand cases, prefer naked). Spec wise the Rezound is the winner, but every time I'd compare the two side by side, I just didn't feel like it was a worthy upgrade. Although the Rezound's screen is better I didn't like that it's narrower (phone itself is physically narrower as well). Also didn't like the red accents or the feel of the power and volume buttons (prefer the metal accents on the Thunderbolt). They're black and smaller than the Thunderbolt and felt cheap. Also didn't like the back cover of the Rezound, looks ugly (subjective I know) and the speaker cut out looks cheap (compared to the metal grill under the kickstand on the Thunderbolt). Overall, the Thunderbolt felt more solid in hand, better build quality. If given the choice, I'd still stay with the Thunderbolt. Anyway, just my two cents.