When looking at new electronics, the Motorola versions just always seem to be most ideal for me.
I'm on AT&T, my first Android phone was the Bravo, and then a month ago my wife took that phone and we bought an Atrix for me.
Before I chose any of my phones, I looked very hard at the different options. In my opinion, the Moto options I've looked at normally have the best blend/choice of battery size, screen size, build quality, and hardware specs.
I do not like large screened phones. The ideal size is 4" imo.
I personally do not like SAMOLED screens. Every Galaxy S phone I've looked at has a really weird blue color to it when not looking directly at the screen, which gets on my nerves constantly. Also I've heard many more hardware issues with Samsung phones than the other manufacturers, which leads me to believe they don't use as high-quality parts.
HTC makes solid quality looking phones to me personally. My big problem, and the reason I won't get their current offerings is they are known for putting the smallest batteries possible in their phones, and I hear constant complaints about their battery life.
The only issues I have with Motorola are Motoblur, and the locked bootloaders. I have never turned on any of the social network aspects of Motoblur, so it really doesn't have much of any impact on the usage of my phone, although I wish I could more easily access the "helicopter mode"/zoomed out view of my homescreens, and get settings toggles in my notification bar. Other than that, with Eclair/Froyo I liked the size and position of the phone icon, and with GB the UI seems to be little changed from what I know of vanilla Android.
The locked bootloaders have not affected me, because although I have my phone rooted, I have not gotten into the whole ROM'ing scene yet, but if it produces a more reliable product (I have no idea if it does), then I guess it's probably for the better, although geeks who know the risks should still have the option to tinker.