Eh, just do whatever you're most comfortable with. MM is technically the best end game dps spec for hunters but it's really up to you. You could switch to MM and lose 2-3k dps because you won't be comfortable with it. BM is still viable too.
I'm familiar with the SV rotation, I have my UI tuned so that it works for me, I know how to move during raid fights, I'm familiar with my utility abilities. Theoretically, an equivalently skilled MM hunter would be a few hundred DPS above me, but even if I was magically able to make an immediate switch so that I saw a target dummy DPS gain, I'd lose in all other aspects (heh) until I was up to speed on everything else beyond rotation.
And I doubt if I actually would see any improvement, personally. From what I've read of the MM playstyle, SV is a better fit for me.
Pick what works best for you. The three specs are more balanced now than at any point in history. That wasn't always good advice - there were times when you had to swap to the FOTM raid spec because the gap was too large. But not right now.