This is really useful for those who are new to pet battling. I remember some of them well because I use those classes a lot, but some of the other ones I struggle to remember. This cheat sheet is from Warcraft Pets made by Perbethril. Thanks so much for the summary and pretty graphics!
My classes that I use have tended to be beast, mechanical and flying. I think it's really important to have a healing pet! Crystal Spider is my healing pet of choice, which is why I'm trying so hard to get a rare one :D
This evening I finished battling all the Kalimdor trainers. Fortunately, none of them had all elementals as pets or I'd be in deep poop!
Defeating them opens up a daily to defeat Grand Master Trixxy in Winterspring who has a flying, a dragonkin and a beast as her pets. I beat her twice to get my Clockwork Gnome to 20. Woot!
Then I headed to Outland and picked up all the pets in Outland to get the Outland Safari achievement. The Sporeling Sprout was my last one to get - it only spawns in Sporeggar and the first time I went (night), there were none around, but the second time I went (early morning) there were about 4 around.
Soon, soon, soon I can start to battle whilst I'm in Pandaria! Not long to go!