Well. If you are looking for a good OHK sniper, you should try to get Mosin because of its high 1 hit kill rate. But Mosin has a bad scope for long range, however it is VERY good at quickscoping. But reloading takes a good amount of time, also quickswitching time is very good.
Kar98k is only good for its good looks and its awsome shot sound. If you want to get that gun for a OHK, don't because you will regret it, also the reloading takes forever just like on Mosin.
TPG-1 EPKO is good for camping + quickscoping. If you have used TPG-1, you'll notice its scope speed is slow but on AP capsule version it is little bit faster. Also it is a clip gun so it can be reloaded faster.
Silver Arrow is good for its looks too. It kills with one shot about 90-95 percent of time. It also is a clip gun and has VERY fast draw speed.
Alligator is almost like M4A1 MK3 but with a slightly less recoil. It is very effective in medium and low range.
If you want to try these guns out yourself, I definatly know the bots are equiped with Mosin and Alligator in "AI Normal." So you can pick them up and try them yourself.
If you are a starter at the game, I would first try to win Desmodus. But if you have played this game for a good amount of time I would go get a FG42, because it can wallbang. But be carefull, with a great wallbang, there comes a great hackusation.