If you're wanting a sniper rifle, be prepared to drop a lot of cash into it and a ton of time to get it working right. 99% of people get a sniper and still get out ranged by standard guns.
TM/JG VSR 10's are the most popular sniper rifle as they are light, easy to work with and have a ton of aftermarket parts. Once upgraded and tuned they perform very well. Well/Warrior L96 platforms are also pretty good, have a load of aftermarket parts etc but at noticeably heavier.
You'd do better trying the "role" of a sniper before investing in a rifle as most people don't appreciate how different and difficult it is, resulting in them giving up after spending a ton of cash. If you got a mate with a rifle, borrow it of them first.