I have not yet tried Xperl but pitbull definitely gets thumbs up from me. That is about the only mod I could not live without. I configured it to display all that on party leader display:

1) show hp/mana/castbar of everyone
2) show everyones threat to current target as a bar (except the tank)
3) show everyones target and its health bar, plus the targets raid icon (so i can quickly see if everyone is targeting the right thing by looking at icon). My tank attack macro always sets the skull icon automatically.
4) My targets hp/mana/castbar and its buffs and debuffs. I made buffs REALLY large because boss/heroic buffs can be huge (reflects etc) and you have to know about them.
5) Adds a colored border to party displays when they get cursed/diseased etc. I picked one color for stuff that palys can cure and another for curses (mage decurse).

Plus I configured the colors: health green, missing health red, mana blue, missing mana black, threat bar: pink. Also when somebody (other then tank party leader) gets aggro their whole health bar turns red. This way If I see any large amount of red, it is bad and I know to immediately take action.

I also set up targets target bar to be colored by class. Paladin class is green and mage class is red so if the mob switches from tank to a mage I get a big green bar turning red to help identify the switch.

Ziran