Since announcement of Paragon 2.0, everyone is busy farming XP. It doesn't matter which toon you use for leveling and ultimately all classes will attain the same Paragon level you achieved after converting to Paragon 2.0.
The favorite class for XP by ranking (in group play):
1) Barb - can reach P100 in less than 50 hr by using WW, Rend-Ravage set up.
2) WD - Locust + BBV
3) Monk - Cyclone Implosion + Overawe
4) Wiz - Archon or Meteor
5) DH - none
This can be witnessed by soaring Skorn prices in AH, with LS + CD.
Just for your information in case if you don't realize it.