I would recommend anything that's not a scope. If you choose anything besides a Squiffer, you're going to need at least 2 damage up. Squiffer has the fastest charge if no damage up is factored in.
For me personally, I got great practice in the testing facility. I would try to kill my targets with the minimum charge and at weird angles. I would also practice moving around and shooting, and even jumping. If you're going to use my practice, try to keep all dummies destroyed while constantly moving. You should also practice twitch aiming. While you're charging your shots, don't put your cursor on the target until the minimum 1 hit charge is ready. A good exercise is to try to stay under 110 damage.
I would not go into gaf room with no experience with chargers. Constantly dying while getting no kills would frustrate me which will then make me play even worse. Once you've gotten aiming down in the testing area, practice against random players. Try not to sit on perches or the usual sniping areas. You will find more success hitting people in areas they aren't expecting.
