That was a quick response. Specially since it was onna Sunday.
The TOPO US 24k mapping is more detailed in almost every way. An important distinction between the TOPO US 24k and the TOPO US 100k is that the 24k mapping includes routable trails and roads, whereas the 100k map does not have routable trails and roads. This may impact which trails are viewable in the map. What area are you in? I will check the available trails on both mapping products to double check the available trails.
With Best Regards,
Product Support Specialist
913-440-8280 (fax) Att: Christopher Bl., Associate #5842
Additional solutions may be found at http://www.garmin.com/garmin/cms/site/us/support/searchsupport
So it seems that for trail riding the 100K is better since it provides more trails, while the 24K Topo only shows the trails that are routable.