You get exp from kills your minions get.
Also, Siege minions are incredible. I use them for offensive support, I use them to break towers, I use them to harrass enemies, and I use them to creep while I'm returning to the base. They're so good that I wouldn't even consider not using them.
Minotaurs aren't as useful as sieges, but they make good meat shields against towers, and the damage they add isn't terrible.
Priests have great damage capabilities in addition to healing.