Ideally, slower is better to maximize DPS. For tanking, I would focus on having the main hand be slow, then the offhand slow also. If you don't have an alternative, got MH Slow, OH Fast, or MH Slow, OH 'stat stick'. Problem currently is that most tanking weapons are itemized towards 2H or warrior/paladin mechanics. I can't think of a respectable 'slow' tanking 1H, so you may end up using a MH Slow DPS weapon, with a OT Fast Tank weapon.