I'm pretty unstoppable at Sniper with the huntsman and jarate, the one thing that bothers me a lot is a Soldier at close range.
Close range rockets can almost always mean a quick death. The best tactic is to run, dodge and put some distance between you, unless your jarate chop is ready and the soldier is unaware.
Also Scouts can be deadly if the scout player is highly skilled, though clever tactics can take away a scout's advantage by using bottle necks points to time attacks.
Finally, a skilled sniper at long range with the rifle will usually beat a skilled sniper with the bow, unless one attacks from different positions constantly. Also the bow usually trumps the rifle at close range and they are somewhat even at medium to long range.