Long toss. It works because
1) you cannot throw at maximum distance unless you have good mechanics. So it reinforces proper mechanics through repetition. These (efficient) mechanics will keep your arm healthy and maximize velocity.
2) It also keeps your arm flexible as muscles and tendons air out.
3) It promotes arm speed. You can have the most efficient mechanics in the world, but without arm speed you will never throw 85+.
As someone else stated in another thread, it is a good idea to use bands to stabilize the shoulder and back and aid in the deceleration process. An arm is only as fast as it can stop.
My suggestion: Long-toss year round 3-4x week. Throw 5-6x week. Lift weights (no lat pulldowns or bench presses) especially concentrating on the lower half (legs). Get on a solid plyometric program for core strength and rotational efficiency, eat well, sleep right, and stay in tip-top cardio shape. Finally, get a qualified pitching coach to work with in the offseason to perfect your mechanics.
This is what has worked for Bum, Jr.