I've always been BM. The other two trees didn't even occur to me until a friend pointed out it wasn't optimal for raiding/dungeons/whatever. (TBH I didn't even realize there was more than one tree to choose from at first so I guess there's always that.) I tried out MM (which was optimal at the time) and SV (when it was optimal), but I'm a BM hunter at heart. It just speaks for who I am. I love the idea of being at range, period, because guns are awesome (started as a tauren), so the other specs are fine and I enjoy them but just. I like the idea of leaning more heavily on my animal companion that BM implies. Once I figured I really am not one for raids or dungeons except occasionally and casually, it just didn't seem worth it to use the other specs. Lord Kri is, hands down, my favorite pet on live.
I am. Though I'm disappointed by how people are reacting to an exotic pet getting a battle rez. "How DARE BM hunters get something so cool and useful!"
I guess some folks can't be happy when other folks get something cool.
But definitely still sticking with BM, even if I was a total MM person in Vanilla.
Sofia, the remarkably purple spirit cat as drawn by Ket Shi.
I've always been BM, although I did go Surv in BC endgame when BM was pretty bad. in Wrath secondspecced into BM and never really went surv again. Right now my first spec/offspec is MM, because I wanted the interrupt for challenge tames, but I' wouldn't play MM, it just doesn't mesh with me.
Ironically before Wrath endgame I never used any other pet than my first tame, Infected nightstalker runt Ramu.
Hydra sig by Vephriel, may this hydra soon befriend Sherbe!
The only time I switch out of BM is for PvP and I go MM, but even then that's not guaranteed. I love my Loque and my Nuromoc too much to not bring them into BG's with me. I've gotten exceedingly good at being BM recently, and switching out would just feel odd. but on the good side, BM is now a 'valid' spec again, so I'm not complaining.
However, play what you like, and if the means MM or SV, then go for it! I think Cata has balanced each hunter spec fairly evenly.
I've always stuck at being a BM hunter. When I started to understand talents better as I was still learning, and tried out suggestions on how to spec as BM from that hunter site, I found out how much more easily my pets can get the job done quicker for me. They don't die as quickly and they can rape everything.
I have only gone to MM as an offspec for a bit more dps but I've always wanted to prove BM can be just as strong.
Bm has always felt like the spec for me along with surv I never really felt for MM I've been playing a hunter for around 7 years and most of that time I've been Bm.
The old AV was the most fun I'd own everyone as Bm even when MM was the best spec I stayed Bm coz it was my fave spec.
It's currently my fave spec because of the awesome pets you can use however it's not so much fun in cata because pets can't change spec and so most of my fave pets are tanks or cunning and I never quiet liked cunning for pve, either that or people want buffs and so I'm forced to use my cat or wolf and so I've stopped playing retail because I've fallen in love with my beta hunter and his goat.
As sad as that may be but once MoP comes out I'll love my hunter all over again, I've cleaned out my stable of pets that I won't use anymore they all said there farewells as they went back to the wild and I will add goat, quilen, water strider, caterpillar, porcupine and new tiger to my stable instead as I've already made friends with them oh and crane and maybe a croc, I also want a hydra and some more pets I've seen but I guess we will see if blizz let's us have them this time around or not. Hopes.
BM has always been my main spec. Back in WOTLK the Horde guild my main toon was in (before I wised up and moved on over to the Alliance) insisted that I raid as a MM. I hated it, but back then I did a great deal more DPS as a MM and I wanted to update my gear so I went with it.
Ever since moving over to the Alliance, right before Cata came out, I've kept my spec in BM on my main and have not budged. The other specs are fine-but not nearly as entertaining to me. I've leveled other hunters and tried the different spec-but just couldn't get into it. With Gojira, my bright green devilsaur, I've run raids with equally geared hunters in other specs and came out top-it is not just the spec but how well you play it as well. BM are not, in my opinion, great for getting a high DPS in a small amount of time on a single target-the other specs out do use there I think-but when it comes to the long term combat, it feels like BM comes out on top.
My sister plays on another server as a frost mage, and she is always bragging about how op she is-we ran an instance together, and yeah one the start of a fight she was outdoing me-but as the fights wore on, she dropped lower and lower on DPs while I kept going up.
Now with Pandaria coming out, it'll be a bit different and more just what you prefer. I've been playing a BM in Beta, and while I do enjoy it-there is more variety there for you to mix your spec into something more hybrid. Ex: BM spec with chimera shot? MM with fervor? It will be interesting to see who pick BM and what level spells they pick out.
BM Hunter all the way here! I have just never enjoyed the other two specs nearly as much. Add to that I'm a zoology/cryptozoology nut irl, and, well, there it is. It also helps that I'm typically in the top 2-3 on the dps charts in my guild's raids.
The latest addition to the team, Jaxo the goblin, I took Survival, and I'm not permitting him to dual-spec. The reason for this is two-fold. First, I don't want to let myself wimp out and give him a BM offspec, since part of Jaxo's grand experiment is for me to learn how to play Survival at least somewhat competently. The second part of his experiment is for me to assemble a stable of "cool-looking," "shiny" pets that aren't exotic and don't require BM to get. It's sort of my attempt to prove the point that you don't have to be a beast master to have an awesome looking stable and an awesome-looking pet by your side.
That being said...gods, have I gotten grief for being a beast master in the past. Now that - at least on Normal setting - the 3 specs are close enough in damage that you really can play what you like, Tufak and I are usually neck-and-neck at the top of the meters, with him on Daashi the survival hunter, and me on Tahl in BM.
Tahl's collection of felines has come in useful too, after a fashion. It's now my "raid job" to bring a spirit beast, to help take a tad of the pressure off the healers, unless we need a different pet for a specific purpose (Houston the core hound if we're missing Bloodlust, or Cinders the dog for Lock Jaw on the goblin sappers during Blackhorn phase one). And believe me...when one of the spirit beasts isn't on duty, everybody notices now, I've found.
I'm definitely a better marks hunter than a BM one, but I like seeing my exotics every now and then. T_T
Sofia, the remarkably purple spirit cat as drawn by Ket Shi. 
