is probably a really good starting point, since the Pandaren trainers are one of the best ways to level more pets. I really wished that I wasn't being stubborn to take a long time to level them since a lot of these pets are also used in the celestial tournament too.
Another thing that I've done was learn about the coming trainers and then leveling the pets to counter them.
If I were to go over your list, this is what I'd pick instead:
1) Mechancial - Darkmoon Tonk
2) Critter- Rabbit or Snail
3) Beast - Spider (especially one that would eventually have brittle webbing and swarm)
4) Dragonkin - Infinite Whelping/Celestial Dragon (The celestial dragon had won like most of my battles when I was doing the trainers)
5) Elemental - Terrible Turnip
6) Undead - Spirit Crab/Crawling Claw
7) Humanoid - Anub Idol/Peddlefeet
8) Magic - Shimmering Wrymling
9) Flying - Moth
10) Aquatic - Crab
However, with that said, I leveled like three of each class and eventually gave that up and just leveled to beat the trainers. Honestly, I ended up abandoning most of the pets that I started to level in favor of the ones I ended up capturing, especially when I was in Cata and Pandaria