as you progress through the task and complete stages, you will get small messages about recieving rewards. Those stage rewards are given to the toon who are in the instance at the time of completing that stage, and are stored up until the task is completed, adding to the end reward.
Thus, the toons you zone in at the end.. are only getting basically 1 stage worth of XP/money, while the toons who were there the whole time got all of it. This was a change put in specifically to counter what you were doing ( they also lowered the XP gained from killing NPCs in the instance at that time as well, while increasing the task reward to compensate... so it no longer payed to drop the task before ending just to loop the instance for relatively safe XPing)
_____________________________
as for leveling... if you have not gotten your toons into RoF gear, sitting on some named in RoF to gear up would also be decent XP. Otherwise.. since the DH mission scale down to 85 now a days ( as I understand it, have not specifically tried it out) running your toons through those is a good idea... provided they can do it. Remember the mission scales to the highest level toon in the group.
Otherwise... if you are tryng to PL... any sparesly populated zone that is just over your lowbie toon levels that your PLer can handle ought to work. Like... CoBronze... Sepulcher...EW....Chaperhouse.. all depends on your server and what folks like to do on it =)
