It depends on what you want. Hub gears are easier to keep clean if you ride in sloppy conditions, but depending on your setup can make wheel removal for flat repair a little more involved. Internally geared hubs are not offered as commonly on as many different types of bikes. Derailleur gears won't shift if you're not pedaling, so it requires a little more advance planning when you stop at intersections. (Oh, this is NYC - maybe I should say IF you stop at intersections! )

You'll hear a lot about how derailleur gears need adjustment - I find that mine need 30 seconds of turning the adjuster nut once a year. An internally geared hub might require a little turn of the adjuster nut once a year or so to take up cable stretch - pick your poison.

Honestly, I'd pay more attention to finding a type of bike I liked before worrying about what sort of gearing it has. If you find you're really attracted to a particular bike, there's no reason to not get it because of the gearing system it has.