I'm one of those who likes topo better. For one thing, the maps don't require 'unlock keys'. My understanding is that the City Navigator software is locked to the GPS unit on which it is installed. In the past, Garmin has provided two unlock keys with the software, but there seems to be some question about whether that will continue after June 1. I just upgraded my GPS unit after having the old one a month--I would have been pretty upset if my maps had been locked to the old unit.
If you get topo maps, do be aware that they don't show streets in the same level of detail as Garmin's street maps. Their primary purpose is to show topography--elevations, streams, and so on, but not trails or paths, or even all streets.
To get an idea of what Garmin's topo maps show, you can go to their website and view online samples. It's the best way to avoid disappointment and frustration when the topo map doesn't show the trail that you are on.