There are well over 600 pets (although many are nearly identical) to choose from when pet battling. Some are much better for battling than others. In fact, there's a pretty accepted list of what the "best" pets are and even this website ranks them (not that there's anything wrong with that.)
So I decided early on that I didn't want to just use the "best" pets. Just following the trends of the meta or what worked best for the Celestial Tournament would be more like following a script than exploring the wide array of pets available. Instead, I would only level and play pets if I really liked their appearance and/or they had an interesting move set.
When I got my first 10 pets leveled (1 of each type, chosen based entirely on their looks) I was able to beat all the Pandaria beasts of fable and trainers. When I had about 35 pets, I beat the Celestial Tournament. Again, pets chosen basically only for their appearance, without regard to abilities or stats for the most part.
I'm up to just over 100 pets now but I still stand by my policy. Every so often I "trim" pets from my favorites list because they just stop doing it for me, for whatever reason. I only want to use pets I like.
Occasionally this is annoying. I am not a huge fan of the Mechanical Pandaren Dragonling, but I am super tempted to level and play one simply because it is the #1 most used pet in pvp pet battling that I come across and it wrecks my team 9 times out of 10. But I will not give in...
So do you have any sort of policy like this? After all, with the exception of a few very exclusive pets, we all have access to the same pets. Which ones you play is the only way to define yourself.