Last I checked, mine pull some additional items that Talky doesn't, and it is styled in a UK-familiar way; it also has a special icon for bike shops.
I started mine because I wanted routable and topo together, wanted fast updates, and didn't like the standard Garmin style or any of the candy-box alternatives that were around at the time.
Try a few, see what you like, that's the open source way; I know some people who use both the OSM and the Garmin, swapping out SD Cards (they're cheap and tiny) for different uses. In particular, if you're globe-trotting, I heartily recommend Cloudmade, who have a (very vanilla, no topo) set of maps for the whole damn planet.
Fresh OSM maps will have new stuff that year-old Garmin maps don't, and if you don't update for years because of the cost, you'll be missing that new housing estate / wind farm / space elevator.