I tested a bunch of roms, Slim,Vanir, Pac,AICP, Beanstalk, Mokee, Avatar, Omni...Some 4.3 Some 4.4
All I can say that I really liked most 4.3 roms, but their battery performance was weird-lacking.
I dont really like KitKat 4.4 that much but apart from the early CM11 releases, most 4.4 ones are battery friendly. I get decent battery life.
I had one day at 8 hours, 2 to 1:30 hours screen on time, and in the end of the day I had 20-30% left. Thats ok for me.My battery is nearly 1 year old now, so they fared good.
That said. I think that KitKat in general does a better job at memory handling aswell, I get always 500MB free memory in most 4.4 roms.
IN 4.3 roms, that wasnt always the case.
Whatever the case, my conclusion is that newer roms, that have been ported recently, fare better because they are based on latest CM builds. Earlier roms, which were just ported to our device...well...it depends.
My testing was so that I tried each of these roms for 1 day. Maybe thats not enough, so dont go around bashing me for inaccuracy. Best way to test things is to try them out yourself. I never tried any benchmarks on these roms because I dont care about benchmarks.I usually set animations to off or 0.5 on each of these roms. I dont play games on my phone aswell.
Personally, my recommendation is to try out 4.4 roms firstly, then try out earlier roms.
I currently use a CM nightly.
Keep in mind however that I do NOT use google play or any gapps. So most if not all ROM experience has been smooth, with the exception of 1 Rom.
I can name it, but that would not be fair, but I think that one came together with Gapps.
So my other advice is that gapps are huge memory hogs and battery eaters.