Repost from me from the official forums

[Sonata]

All 3 trees playing the same is bad, because it ends up with every hunter being speced the same, no variation. If all 3 specs play the same, then Whichever is the highest dps will be what people use.

Not to be rude but THIS is the worst thing to say...take a look at the rogue, what do their trees make a difference to eachother? Even if they choose a different tree they STILL do the same skills and so on and deliver the same white duelwielding damage of doom! Hunters are meant for one role last time I checked, ranged dps...hunters are not hybrids like paladins and druids who can do three roles.
Even if Warlocks go into Destro they still keep an imp for buff...

But hunter/warlock (not imp or succubus sadly D:) pets have been proven to be good offtanks and saving healers, heck some even tanked a whole instance. But having a pet makes the hunter and warlock classes unique.

And there is a difference in the way the different trees do damage, BM has the pet as the hunters biggest damage dealer, MM deals burst damage (similar to a mage), while Survival is steady dps on it's own. I'm not sure how the damage output was for survival but I think it is a steady dps outcome.

Hope I'm not trolling! D:

[Golden]

No one dual specs any points into BM except for the slight DPS boost.

... *raises hand* BM/BM main here. And if I may say, I don't find the three specs all that similar. As BM has a bigger reason to micromanage its pet, its shot rotation is a lot simplier and it has more mobility due to the pet often being able to keep on dpsing while the hunter has to move or turn to take care of something else. Now, I only know MM and SV in theory, but SV is more about traps and being stationary (Sniper Training), whereas MM is more like BM but a lot of the damage is moved from the pet to the hunter. SV's rotation is also all about procs, as opposed to BM's priority list that stays unchanged.

Again, I've never seriously played SV or MM, but have been reading about them quite a lot.

[Azunara]

I've played BM 1-80, and then went Surv.

Survival gives you a lot more different shots, (which is as far as I can see is the difference.) BM focuses on your pet and the aspects, and MM...I think their only use is the Aura. Correct me if I'm wrong, the farthest I went in that tree was for Go for the Throat.

And I'm a proud Surv/BM and I love my pets. I always feel guilty when I have to run away cause the odds are awful. They all have names, and they have stories. I went through two rename scrolls to find Arturis's perfect name, and he's the only one who lacks a story since he's new.

I'm done, that's my take. Prolly what everyone else has covered.

[Anansi]

Survival gives you a lot more different shots, (which is as far as I can see is the difference.) BM focuses on your pet and the aspects, and MM...I think their only use is the Aura. Correct me if I'm wrong, the farthest I went in that tree was for Go for the Throat.

You're wrong

Marksmanship differs significantly from both BM and SV. Trueshot Aura is one difference, but Marksman also provides Readiness which is a massive tool allowing the player to get more use out of their longer cooldown abilities (eg Rapid Fire, Disengage, FD, traps) which provides fantastic flexibility. In this, MM is more proactive with procs and CDs than SV which is more reactive to them. Marksmen also make more use out of physical damage than Survival, meaning they benefit strongly from the Armour Penetration stat and can use that to their advantage by creating larger Piercing Shot bleed damage and removing a mana-consuming shot (Arcane Shot) thus giving them a bit more longevity outside of Viper.
Survival requires the management of DoT effects via manually applying Serpent Sting, Black Arrow and watching the ticks of Explosive Shot, while Marksmen do not need to to do this as our DoT (Serpent Sting) is automatically refreshed via Chimera Shot. This has a couple of great advantages - we do not need to watch ticks and micromanage those DoTs, the 2 piece T9 bonus is hugely beneficial since the Sting has a 100% up-time and with procs like the 2 piece T10 we can enhance our Serpent Sting damage by manually re-applying the shot and continue to benefit from any damage increasing proc.

So Marksmanship definitely has a greater difference in play-style from Survival which extends far beyond TSA.