Ive got a lot of lvl 25 pets now and i tend to use a lot of different ones. However my team setup goes something like this:
First slot: An avoidance type pet. Because they are really needed if you meet a burst type.
Flayer Youngling and Arctic Hare tend to be my choices. The flayer has reflection, and the bunny is fast with dodge and burrow.
Second slot: A high damage pet. The pet that smashes things apart asap.
Li'l Deathwing, Darkmoon Tonk, Disgusting Oozeling. I plan on using my Enchanted Broom sometimes once ive found a rare stone. That sweeping and speed seems insane.
Third slot: A tricky pet
Frosty, Crawling Claw, Peddlefeet. Basically a pet with something special. Undeads can ress for another turn, so i like to use one as a last resort, or to do other stuff. With tricky, i simply mean a pet with some random trick up its sleeve like a stun or so. It can be any of the other two categories, or something else like a healer.