I have seen a Bard Warlock on lvling, he put 2 Dots and ran to the next mob, and with his amazing Speed he lvld freakin fast. Along with your shield and a good set you will almost never die. This build is also welcome at parties (either you play bard, or debuff the mobs if necessary) also at Fortress Wars, but its pretty weak on PvP since you got a big disadvantage compared to subclerics.
A Bard/Cleric is lvling fast, keeps his HP MP up by itself and do not need much of Pots. Very asked at every party, you are simply a fullsupporter.