I would want the rack to be close to my site -- even part of my site, so that I don't have to leave the bike out of sight. The best racks seem to be the ones that make the fewest assumptions on how a bike must be shaped. At my work I sometimes am unable to get a spot at the long railing in the bike lockup, and have to hang my bike by its wheel on one of the vertical racks. Those things are terrible because if hung by its front wheel a U-lock doesn't reach the rack's U, and if hung by the rear wheel the rear derailleur comes in contact with the rack.

A U rack is simple and effective. I'd go with that.