Individual map updates are simillarly priced. Subscriptions are done differently. Garmin offers a one-time payment lifetime map update program, up to four updates per year no additional charge for as long as you own your nuvi. It can be found for as little as about $85. TomTom does a yearly subscription for about $45, plus the cost of bringing your current map up-to-date. Keep either for roughly two years or less and the costs are pretty much the same. One big mapping difference: TomTom offers IQR, a database of historical travel times broken down by time of day and day of the week. Garmin's Navteq routing does not yet offer anything similar, tho that should change this fall. For now, IQR gives TomTom a leg-up on up to 35% of trips. But also note that in some parts of the country TomTom/TeleAtlas is still playing catch-up in the quality and quantity of mapped roads compared to Navteq (Garmin). But a few areas do have better mapping than Navteq has. IMO, in general Navteq offers more reliable mapping in North America overall, but not necessarily in your specific area.
All the TomTom's I've used have very good touchscreens, so that shouldn't be any concern. On to maps, TomTom has a very closed system for them. It's going to be tough to add any maps that don't come directly from TomTom. Garmin's on the other hand can use thousands of 3rd party maps from marine use to topographic to off-road and user generated maps of out-of-the-way places.
There are so many differences, we could fill an entire page. A good friend of mine, Infama, and I had a
very long discussion on the merits of Garmin vs. TomTom two years ago. (Of course that was back in my very pro-Garmin days. . . I'm a bit wiser now
). Most of the points we made are still valid so it might be worth a visit. The latter part of the posts (bottom 3rd) cover the differences more clearly.
TomTom GO 920T vs Garmin Nuvi 770 -- NaviGadget