I bought the TomTom Via1605 a year ago, it had a 6" screen with good screen resolution. I traveled with it for about 6 months and was happy with it's size, lane view, speaker volume & clarity. The Mexican maps were good and it came with lifetime map updates. All GPS units make mistakes in map routing so I stay with my routing using MS Streets & Trips which is easy to put in vias to get you on the route you want to take. Two problems, you can't upload the MS routes to the TomTom and the map download process was slow and fraught with difficulty. I accidently erased all the maps, needed lots of really bad support and could never get my Win7 laptop to update the maps only my WinXP.
So this year I bought the Garmin Nuvi_2797LMT. It has better Mexican maps with a very easy to use lifetime map update. It can upload GPX files from your MS S&T so that it takes the route that you planned. It's routing of fastest route is poor. I'm often on a route and don't take the route that it directed and after it reroutes I find that it says my new route is faster. Why didn't it choose that route to begin with? The 7" screen is great for RV's, I can plainly see it, even in bright sunlight. And if you can get along without Lifetime traffic,
Bluetooth, & Voice activated navigation, you can buy the Nuvi_2757 LM for only $220 from Amazon with free shipping.
Compare specs on 2797 & 2757