For me definitely the 5.xx. UT is more playable now and some other things were fixed.
Asus P9X79-Deluxe, Intel i7 3930k @ 4.2Ghz, 16gb DDR3-1600 Kingston HyperX Memory, Coolermaster Storm Trooper case, Corsair AX850 psu, Geforce 680 SLI, Corsair Model H100 w/c, Western Digital Model WD2002FAEX 2TB, Asus Blu-ray Writer 12x, Windows7 Pro x64
What are you looking for more? FPS or Stability? for me, i got higher FPS with 5.13, but i am SUPER stable with 5.22. Also there are better bug fixes in the 5.22. I don't mind loosing 3-4 FPS for having better stability. The only draw back i can see to teh 5.22 is that the little "NVIDIA" logo is always on in games. Even if you uncheck it in Advanced settings, it is still there. other than that, i say 5.22 are the best for my TNT-2 Ultra.