[EricH]

More to the point, Chris, is "what resistance to normal motion do swivel casters give you?" I've heard the horror stories of teams using them, only to have their robot go a little crazy when a caster didn't act like it should have.

I've also seen teams use ball casters with some success; most teams opt for omni wheels of some form instead of casters as you can get a little bit more forward "oomph" from omnis.

Short and sweet: swivel casters won't give you any less resistance to being pushed around; in fact, they might be the ones doing the pushing. Ball casters are better about not pushing you around. Omnis give you a little bit more forward/aft push (though not much).