I believe that all the Beasts of Fable come from three groups: Critter, Beast and Aquatic.
I haven't bothered much with defense I'd rather finish them quick, so what you want is something with high powered Beast abilities for the critters, something with Mechanical abilities for the Beasts and something with Flying abilities to deal with the Aquatics.
On average I need more than 2 pets to beat the legendary pets. So you need three of each type. Rares are definitely to be preferred, especially for capturable pets.
Good and easy capturable pets to beat the Critters:Kun-lai runt
starts at level 20+ Alpine Foxling Kit
starts at level 20+
Any type of snake, while I haven't used them they appear to do a lot of damage to my pets for example Elder Python
Not quite as easy to obtain a rare of are Flayer Youngling
and Stunted Shardhorn
Pets to use against the Beast types:Clockwork Gnome
- you have oneCogblade Raptor
- starts at Level 18-20 ...
Your armory profile says you have a Lil' XT
- it is my most used pet against Beasts
I like to accompany my Mechanicals with a pet that has Call Lightning
- I like to use Wild Golden Hatchling
- this can backfire however in a bad way (it's allso very good in combination with any multi-attack and dots, just look at the Firefly abilities)
Pets against the Aquatic types:Jade Owl
- except for that fishy with the frozen dragons breath. Try to stone the Owl ...
Any type of Moth for example Luyu Moth
Any type of Firefly for example Effervescent Glowfly
The fireflies also do very good against many of the tamers aquatic pets ...
Other than that I really look forward to trying out the Life Exchange combo several people suggested.