pink tallstrider.
For me its Gondria. She was my first spirit beast pet and I've made a BM spec specifically for that back in Cata.
My rare pet Sambas, he looks badass. That and I named him after my son.
Blood elf place where u tame those orangie cat. I tamed it and name it garfield and still have it since :3
My pink tallstrider pet me and one of my fellow hunters who i raided with had matching ones. Just reminds me of a great tier and lots of fun during progression.
My hunter isn't my main but I have a solid white cat on there in honor of a kitten i had that was deaf. Poor little guy was just a few months old, and learned that he had a blood disease that caused him to just bleed out one day at the vet :/ very sad day loved that little guy!
Mine would definitely be the glitch-tamed Sha Scorpion I aptly named "Smoke" that I got right before it was hotfixed. He's my pride and joy and I swear I can't walk through Shrine without getting someone asking "omg how did you tame that" or "where do you tame that scorpion".
It's a shame the scorpion disarm isn't really that useful for PvE but I use him any time I can, or when soloing.
My ghost wolf, and the fucking Worgen pet. Still have the ghost wolf, obviously lost the worgen.
The ghost wolf I got back before the b.net account thing. My sister rolled a hunter on my account, I got the ghost wolf and for her b-day, transferred the hunter to a new account for her. She played it up until...the tier after Ulduar, whatever that was. Her account has long since been inactive. But man, to this day, catching that pet and the worgen both have to be the most adrenaline rushing things I've ever done in WoW. Having to rely on extreme perfect timing and such.
Barring both of those, I have a couple of pets that I managed to catch that have special effects still attached to them. The 2-headed vulture that the Arrakoa dudes summon, has a cool ghostly cloud around it. And one of the crabs I believe from badlands, has a green sort of gas cloud on it. I heard that if the pet ever dies, the effect will be wiped upon resurrection, so I don't ever bother playing with them. I will on occasion bring one of them out to wander around town with. I also caught one of the wolves in ashenvale that change into ghost wolf form, and had him in ghost wolf form for a while. However, one day I randomly pulled him out of the stable to walk around with, and he was back to being just a normal wolf, so I guess Blizzard fixed that one. The bird and the crab still work though.