Well, as you can see, there is one answer for ROM's. Droid-life.com did a survey recently and found that liberty was the ROM in charge right now. But that was before apex 1.4 dropped, so I don't know now.
I've used liberty, apex and darkslide:
Favorite (and highly recommended for beginners) is Liberty. Before you do anything, go to liberty setting and change the "keep in memory" to 50 rather then 25. That will solve the weird reboot issue on a lot of phones. It did for mine, I'd say 90% of the time. Admittedly, I get a random reboot once every 2 or 3 days. But the ease of the ROM makes it worth it, and knowing that the new version will drop in a few week, and KEJAR has said he found the source of the reboots - makes it not worth changing right now.
I've used Apex 1.4. I found INCREDIBLY klunky. So much so that I rewiped everything and reinstalled, and still was shocked at how slow the thing was. I did not like it at all, and was very annoyed with the blur that it kept (if you have a rooted phone, may as well have wycontacts, it's 100 times better and includes facebook sync unlike stock android phones).
Darkslide was okay. I frankly hate the look of it. I couldn't find a single benefit over liberty, so I just went back to liberty.
I can tell you A LOT of people will swear by their ROM's without ever actually trying any other ROM's. There are sub-category android fanboys that run rampant all over these parts. You won't know which ROM works best until you suck it up and try a few.