My favorite is whichever one I'm playing right now. So, I guess although she's already hit 50, my current is my tank Catawampus Turncoat (Rad/Sav).
I'm almost always playing squishies, so a tank is a new thrill for me. I love wading into the middle of mobs and not, like, getting squashed like a bug within a split second. I ran my first Tin/Whatever TF without dying once, and have waded through a kill-most ITF that was something of a real workout for her, but still came through with flying colors. One thing I've found as of late is that I have little patience for having to run from target to target playing melee, so her being Savage Melee means Savage Leaping from one victim to the next, no waiting! Very easy.