I tried them both, in fact I keep a few backups of each.
I really liked Theory but then I switched to Liberty and tend to spend more time on it...I like the fact that there is more memory available, but you can get the same with Theory and no blur.
There is one thing that bothers me, and it's not the roms, but the firmware. Apparently I am in an area where I don't really get 4G, but mostly 3G. They call it extended something...I spent countless reboots trying to figure out why there is no network signal. I also had a defective SIM card, but even after replacing it, I had the same issue. The key was setting the network to CDMA only. If I am in a good 4G area, I can switch it and it's blazing fast (485 KB/s steady upload rate to FTP!).
Today I tried the latest Theory version 2.1 which supposedly has the new update. I don't know about other people but for me the Verizon update is a big BS. The signal gets lost all the time, no 3G where I know I have 3G, then after a while it changes to 1x, then again nothing and then finally it might catch some 4G. I got so frustrated I reverted my Liberty rom back, which is set on 3G only. I haven't tried 3G only on the latest Theory, however I didn't have issues before. Latest Theory version I ran for a while was 1.8. When I switched to Liberty I think I got better battery life. I have an extended battery, and I used Gtalk with video for about 1 hr and I was down to 75%. Setting was 3G only. I have to mention I didn't lose connection, while today on the latest Theory with the update, in the same area it gave me all those problems mentioned above.
Running Liberty with 3G only, I use the browser, email, wifi, Gtalk, watch Netflix, sync is always on and I still haven't fully discharged the battery. I didn't use the phone continuously, but it was some pretty heavy usage.
Comparing the deblurred version of Theory with Liberty, there are some extra settings in Liberty, however some of them I don't quite understand. You can enable them, but there is no clear explanation about what they actually do.. Theory also has some mods which are more clear: unthrottle, and the others from that script.
Personally, I do not like the launcher that comes in both versions, so I installed GO Launcher and then removed the stock one and changed GO Launcher to a system app in Titanium. It seems to run fine, no errors. I also do not like the contacts app, there is no option to set a group when you add a contact, although I think there is a way to do it afterwards.
Conclusion: the performance was pretty much the same, each rom has some tweaks and customization, you can make them both look however you want, so it's just a matter of personal preference which one you choose. They should both do the job. One thing, Theory gets more updates, while I haven't seen the same on Liberty. I hope this helps.