If its your 1st time boxing then it would be recommended to stick with the same class til you get your wings so to speak. But that doesnt mean its required.

On your list I would say the lock/priest combo would be very good together. Level the priest as shadow to help synergy with the lock and since keep a soulstone on the priest in the event of tragedy you can self rez then rez the lock back easily.

The hunter/mage combo would also be very nice. Frost bolt slows targets down while pet tanks/eats them and hunter plinks from distance. Also the ability for the mage to summon food/water helps cut down on costs and resources. Plus the amount of CC available to this combo is very nice. Got a big pull? Sheep 1, freeze 2nd, pet tanks 3rd, dps down remainders.

There are several viable combinations based on your selection of classes. I think if you were to choose any 2 from that group that you would be happy with the results.