I started as MM because they had an extra shot. At level 60 (back then) SV picked up explosive shot so I switched. Didn't get dual spec until I had been 80 for a while (it was still expensive and I had a spec to dps already). Picked up BM for the novelty of collecting rare pets.
Now...much different. As SV, I have to md my pet and take it a little easy so I don't pull off of him to quest. As BM, I go ALL out and can't pull off my pet. I have him pick up four mobs at a time and it's no prob. BM is the easiest leveling spec of any class IMO.
SV and MM seem to be pretty even depending on how well you understand te rotation.
"he doens't need healing, he doesn't need healing, he doesn't nee-WHAOSHIT!wtf was that man!". Please stop leaning on TDR. -Teng