I'd have to say my favorite weapon is my car, whatever I can drive. I can drive around, kill hundreds of people no sweat, and when my car catches on fire, I park it next to a line of cars and watch them all explode...
Other than that, I'd say the M16(the one that scopes)cause you can blow up cars and stuff really quick. Also the Sniper Rifle cause I like finding an impossible to get to place and sniping everyone I can below, best place to do this is going up the bridge from staunton to shoreside, and as you go around the spiral be on the outside lanes and before the bridge struckture starts, drive off the side right by the concrete thing that starts the bridge girders, you end up on a blueish walkway, so get out of your car, walkout above the street that leads to the bridge, and get out your rifle and zoom all the way and hold it, now move around, find people, and shoot them, like one time each person, and soon you have cops after you, but they can't get to you and you can toss grenades off and blow up the cars below, and eventually you will have to shoot down some helicopters...
worst weapon I think is the firebombs cause most times it catches me on fire, and it rarely goes where you need it to go...
Ohh and also a good one is the uzi cause you can shoot out the sides of your car and start races, just pull up next to someone and shoot like once, and if they start going fast, you can race them and keep shooting them till they blow up, then just find someone else...