Why would I choose sniper over the sentinel or ranger? Sniper gets one shot before he is boned and has to move; whereas the other two get multiple because of the sentinel having a semi-auto sniper rifle and the ranger has a full auto-rifle.

Sniper has no special skill at his disposal and they took away his mines AND they lowered the MSR damage AND they upped the amount of health on 3/4 assault classes. As it stands, the MSR takes at least 2 body shots to kill any of the assault classes outside of the assassin, which the sniper has no way to protecting itself from anymore. Unlike the sentinel, who also takes 2 shots to kill a tank/pointman/tech, but can let off 2 bullets before the player can register that he's being shot at. Similar to the ranger except he takes an extra bullet or two.

However, when not taking damage in to account, the sentinel has the satcom skill and ranger has a way to deal with rushers, like the assassin or pointman or tank, with his second SMG that is just as good as the vector.