220 film is held flatter in the film plane (no paper backing). this is better if you shoot at wider fstops. Less chance of portions of the negative being out of focus. If you shoot at f5.6 or smaller, it won't matter.
220 film will let you get 24 shots per roll, 120 only 12. this only matters if you can't take the time to reload/switch magazines (weddings/parades, etc.)
Since the move to digital for weddings, and the resultant loss of this piece of the professional market, for film manufacturers, I think 220 film will disapear relatively quickly. 120 film will be around for a long, long, time.
Since you only shoot B&W, I recommend you buy two 120 magazines and use one for high contrast subjects and one for lower contrast subjects then develop accordingly.