Garmin now sells both 24k and 100k so you can pick and choose. They also sell via dvd or pre-loaded on microSD card. If you buy the sdcard version I don't believe you can import on to your computer so your better off buying the dvd and then sending it to the gps.
Some of the free downloadable ones are very nice and they will layer on top of other maps if they are made transparent so they can supplement your existing maps.