For a rack, I like the inverted "U" as well. I opted for bike lockers instead for the commuters at our downtown location. Commuter bikes tend to have a lot of easily-removed accessories (lights, bells/horns, pumps, packs, etc.) and having bike lockers allows them to leave all that stuff on their bikes without fear of it getting ripped off. Lockers are a much more expensive solution but, if you can fit them in the budget, they are a much more secure solution.