Being able to slam a virus around doesn't hurt, either. Aside from speedy runners, some slower power is needed to provide distractions and muscle. Soldiers work quite well, but a Sniper or Heavy Weapons Guy are often useful as well. It's really a simple thing to remember, but people seem to forget easily in the heat of battle or a dangerous run for the goal. Demomen are particularly useful for their average speed.
Defensive mobility is helped slightly by the team-controlled laser doorway in the base.
Take advantage if a slower class has snagged the ball. Contact us for more information on GameSpy Industries.