[basilray]

OP - You can pretty much forget about the ROM being a major factor when it comes to installing applications.

The ROM is the core OS, and only needs to be changed when you want to:
1) Get a cleaner option to the Stock device setup
2) Take advantage of up-and-coming features/utilities/tweaks (WinMo 6.5, TF3dv2, etc)
3) Really have fun!

Part of the reason that HTC devices have such a popular following is that they generally get released for all the major Cell providers. They also have a wide range of models that offer different screen types/sizes, keyboards, form factors, etc. That being said, most of us are big on HTC devices because they are more likely to have the combination of form factor and hardware we are looking for.