This is my answer from another thread. It isn't so simple as saying one is better than another, since there is a whole tree of sacrifices you make to get one or the other, and it also depends on gear, but here goes:

To get TSA you lose FI, so to gain 125 AP for your group you lose 3% total damage for your group (okay, a little less since it takes a few secs to get FI up x4). 125 AP is about 9 dps. So if your group dps is above 300 then FI > TSA... I don't think TSA is worth it unless you really need the utility of Silencing Shot further down the talent tree. EW might be worth it if you have the right gear. Personally I like the look and easy play style of 4 BM hunters, and it is just icing that I don't lose anything to do it.

Hunter's Mark is the most important skill IMO for a hunter team -- and that is trained. Four hunters with a fast bow, IAOTH and Serpent's Swiftness increases the AP bonus against a marked target extremely fast. And Improved Hunter's Mark is a must-have, it only takes 10 pts in MM and only 1 of your hunters needs it.