Some retain as much of the original feel of the stock ROM as possible, while others take the opposite approach by stripping all traces of HTC Sense, adding new UIs and apps, tweaking settings, and optimizing almost to the point of turning your EVO into a completely different phone.
The best way to find out which ROMs are best for you personally is to actually try them. As long as you have a complete backup of your current ROM, then flashing news ones is no big deal because you can always go back to what you had before. This way, you can decide for yourself whether all the hype surrounding a particular ROM is justified.
This is what I've been doing since rooting my EVO. I know which ROMs are the most popular—some people can get pretty crazy defending their favorites—but I'm checking out some other ones first. I don't have much "gadget play time" because of my 10-month-old daughter and other websites, so I've only been able to try out two so far: SteelROM RevG and Ava-FroyoV7.
Which ROM are you using?