I haven't played enough campaigns to know what my favorite class is, but I certainly know what the most annoying class for a DM in 4e is, though- since I played it and got no end of raging from my DM:
Shaman
Seriously, the number of feats and abilities you can take or get for a shaman and their ghost pal to debilitate your enemies (damage, lots of status effects, and space blocking) and the fact that it is an instant set of eyes anywhere visible within 20 squares make it, in capable or insidious hands, a DM's worst enemy.
Shaman
Seriously, the number of feats and abilities you can take or get for a shaman and their ghost pal to debilitate your enemies (damage, lots of status effects, and space blocking) and the fact that it is an instant set of eyes anywhere visible within 20 squares make it, in capable or insidious hands, a DM's worst enemy.