That's a very subjective question. I personally prefer Pitbull, because I value a high amount of configurability. X-Perl has a certain look and feel fairly baked in, whereas with Pitbull you can make it look a variety of different ways.
I usually tell people this: if you want an easy out of the box experience with minimal configuration, use X-Perl or SUF or similar. If you want to go all out and create your own unit frames, use Pitbull.