[Samsung Galaxy Nexus] jonstrong:
You'll get lots of opinions. Best deal is if you do a bit of homework and make your own decision. That said...I really don't have time to live on the "bleeding edge" these days, so I try to avoid installing ROMs that aren't pretty mature already. I look for ROM threads with a large number of posts / pages, check the description up front to see if it appeals to me, and then read the last few pages of posts about it. If I see a lot of issues and workaround still being discussed, I stay away from that ROM -- life is too busy these days to spend a lot of time with a half-working phone (although I have no hesitation playing with experimental software when I have the time).

For my own purposes, when I started getting the itch to try out 4.2.1 I homed in on XenonHD, Rasbeanjelly, Xylon and Nexus Evolution. I tried XenonHD for a while, and really liked it -- but perhaps hadn't done a clean enough install as I experienced a few odd issues now and then; also possible I hit it a bit too early before the bugs were worked out. I installed Nexus Evolution 3.0 about a week ago and it's been rock solid, feature rich, and elegantly put together. My understanding is that XenonHD is really solid now too, and I've heard great things about Rasbeanjelly and Xylon as well. I don't mean to dismiss the others that are available -- just that I'm not as familiar with them as the ones I've described here. I'm assuming ones like AOSP+, CM10, etc are certainly worth checking into.

Whatever you do - make a nandroid backup of your CNA install since you like it so much, and considering taking a copy of the backup onto your PC as well just in case you wind up formatting your internal SD pseudo-card. In case you have issues with one of the 4.2.1 ROMs you can always flash the nandroid and be back to exactly where you are right now. Oh...be sure to back up your kernel as well, unless you have installed a known kernel image that's available in case you want to go back to it again. This pretty much takes the risk out of trying other ROMs.

I can tell you from personal experience that Nexus Evolution is excellent on toro, and I'm very comfortable using it after having been a CNA user for several months. I'm confident the others above are also worth exploring - just suggest that you do the homework I describe above to give yourself the best chance at a positive experience.

Finally -- wipe!!! When you're installing, I strongly suggest that you wipe Cache, Dalvik cache, System (this is where the ROM lives) and run a Factory Reset all from within Recovery; I actually run through each of these steps in sequence - and then do it again. Make sure you have downloaded the ROM zip and GApps you plan to install and have them sitting in an easily accessible directory on your internal SD card. Verify the MD5 checksum for each of the files. I have so much "stuff" on my card that I created a separate dir that I named "flash", and I drop all the files in there that I plan to flash during one of these sessions -- makes life easier.

Make sure you have the very latest version of whichever recovery (TWRP or CWM) installed, otherwise you'll likely wind up with the annoying "/0" directory mess and have to move LOTS of files; the latest TWRP and CWMR both know how to handle the move to 4.2.1. There are folks with strong feelings on both sides of this, but after using CWM for a while and then trying TWRP, I generally prefer using TWRP: I like the UI, I like being able to specify multiple zips that will be flashed in sequence automatically, I like the file manager. I've also had some odd behavior on older versions of CWMR in which it created directories that could not be deleted, even by a superuser account, and I wound up having to download and run a special recovery utility to clean up that dir and the files in it. I found it disconcerting that a recovery program would be operating at a level that could munge my file system in such a way, and this simply reinforced my choice of TWRP. That said, loads of people swear by CWMR, and you'll probably be safe with either.

Enjoy! (so much for me doing a "short" post!)