As long as you don't take two meleers you should be fine, although even two meleers can work if you're just doing pve with just two characters, but if you ever want to expand to pvp/more characters you'll start having a rough time. Casters are usually preferred since they generally have good range, no deadzone, and have things they can do even if they aren't facing their target. Their typical low survivability gets covered by killing things before they get a chance to do much damage.

A shaman is a good choice no matter what they are teamed up with. Healing, casting, totems, mail+shield, and even a res and a wipe protection. You can make use of their melee while you pve with two, and can go into full caster if you ever want to expand.