I'm going to compare a little bit of 3 ROMs at once, just because two are relatively simliar, and one is very different. I'm not a dev for them, so clearly Drod could give you much more specifics than I can, but here's what I know about Focused, Blurry, and Fission.
1. All have the majority of bloat removed (depending on what you consider bloat). You can remove most of the rest on your own, if desired. Removing more may cause problems, or may not, and it may or may not make any real difference in performance/speed.
2. Focused offers some build tweaks, as does Blurry, but Fission does not. Each may or may not have minor voltage or overclocking changes, depending on which build it is (this part is a bit more confusing to someone new, because one build may literally be overclocked, and the next release is not). You just have to read the full info to know, or check it yourself.
3. I can't speak for Focused with entire certainty, but as far as I know Fission (which Focused is based on) can't run the ad-hoc wireless tethering. I haven't actually tried it on Blurry, only because I really don't ever find myself tethering, but having used all three ROMs a good bit, I would assume the blur required for the ad-hoc tether remains in Blurry. Someone else could confirm that, or I could hop back to my Blurry build and test it, if needed.
4. Fission tends to have releases more frequently than the other two, and as such each release will likely have more recent bug fixes, and then again, it may have new bugs not present in older builds.
5. All of the ROMs are plenty fast, in my experience. I run a decent amount of widgets, without going crazy. I also have a live wallpaper, but it's semi-static (Weatherbug Elite). I've found that all of the ROMs, without overclocking, perform just fine. Yes, I suppose Focused and Fission may possibly be faster, and/or have better battery life than Blurry, but battery life has more to do with how much your third party apps are draining the system, and how much you're keeping the screen on. If you're downloading tons of files, playing games, or leaving the screen on constantly in general, you're going to run down the battery fast no matter what. Buy a second battery and toss it in the glove box, if you need. That simple trick doubles your battery life....
6. All seem quite stable and reliable, in their recent forms. The important thing is really doing the installation correctly. Know what you're doing. SBF properly, and wipe EVERYTHING. Follow the directions exactly, and read through the posts in the release thread, before you start pressing buttons. I've been able to make all three run like crap by constantly switching between 6+ ROMs, and constantly installing new ones, before settling on one. Once I did, and I decided to commit to it, I did a complete factory restore, SBF, wipe, etc, and it (Fission 2.1) worked flawlessly* after.
*Any ROM, even the stock one, may require an occassional re-boot, or even a battery pull every once in a long while, due to a rogue third party app (which you might consider not using after).
/Using Fission 2.1 currently, have nandroids of all 3 of them, and think all of them are excellent. If ad-hoc tethering were my goal, or I didn't want to find third party apps to replace parts of blur, I would be back on Blurry. Focused gave me no problems in recent builds, and I'm sure I would be just as happy on that, as I am on Fission, with the exception that Fission updates more frequently.
I hope that helps,
-bb
