Heya,
From my experience I would recommend paladin as a tank since they can tank as good as warrior and Sk, have ae heal and good aggro management in general but choose the one you like the most coz at the end they are all capable tanks.
For healer shaman is very good choice for heal and buffs but a cleric might be required for some boss fight, one heal isn't enough without a lot of donors.
As for dps, casters are nice if u don't want to invest into donors, especially pet class since even naked they can give you a good amount of sustained damage.
Wizard are really good but require more attention.
Bard is always a good choice since he will boost all your group.
Melee dps are very powerfull once geared and if you plan to put a few donor on them even more

So it's really up to you, if you plan to play without Mq2 I suggest the following . That's what I run and u can handle it without too much trouble.
Pal/war/Sk * Cleric * Bard * Mage * Necro * rogue/monk/zerker and leave the shm out of the group for boss fight.
If you plan to use mq2.
Pal/war/sk * cleric * Bard * Wizard * Wizard * Rogue/zerker/monk
This combo require more donors to be effective.
As for the donor for Tank : priority goes to weapon and shield then Bp then legs.
And for dps.
Melee :weapon , legs, Bp, augs.
Casters : weapon, Bp, legs.
Of course you can just donate on the tank but If so just go with the first option.
Hope it helped,