pve team whats the best set up for main?

ok let me explain my senario, i currently have 3 dps, all locks at 29 ive decideded to add a tank and healer into the group so i can run heroics solo as i please.

Ive always had one warlock crontrolling the other 2 has been no troubles.

leveling the druid and priest ive used the druid as the main and then just bound heals and casts to my num pad, which is normally where my fears are for my locks.

My question is really what have people found controling the most effective in instances, be it the tank healer or a dps?

thanks

There's only one way to do this if you wanna live basically ^^

Tank as main.