Which GPS depends on what kind of riding you're doing, basically, street maps or off-road tracks.
First for street riding which for me is often long-distance trips across the country to places I've never been to before.
Right now there are 20 Garmin NUVIs at Bestbuy.com that are all under $100. Many of those are 5" screens with free lifetime map updates. Yes, these are not waterproof but the large screens and current features of the Nuvi make them great street navigators. My favorite feature - finding good places to eat while out on the road. Search Youtube for a good video, How to waterproof a Garmin Nuvi. Basically, you just need a small bit of silicone on the edges of the screen. Factor in $40 for a RAM mount and for less than $150 you get a current model Nuvi, good mount, free maps and if it breaks you can buy a few more and still be ahead. In daily use, you can easily send destinations to the Nuvi from your laptop after using Google Maps. My favorite search, "pizza near moab, ut." <grin>
I like the 5" screens but be careful as there are two kinds. The low-resolution screen has larger text vs a higher resolution. With my eyes, the low-res screen at 5" means the text is nice and big and easy to read. Low-resolution costs less too.
The down side of using a Nuvi off-road is you can't enter tracks. You can enter waypoints and destinations but the Nuvi will automatically recalculate the route. That's not good when you want to be off-road and the Nuvi tries to send you back to the Interstate.
For off-road work, you want a GPS that deals with tracks and routes. It's also waterproof and it floats in case your Tenere does not. One of the best current models is the Garmin 78. There are different versions of the 78 ranging from $150 to $300. I'm on the water in boats a lot so I got the one that included a full set of charts for North American rivers, lakes and coastal regions for $300. The key feature of this kind of unit is the ability to load, save and share tracks. Yes the screens are small but when you're following a track you just need to know which way to turn next. The 78 lets you configure your screen to show different data fields in addition to a map and even a simple arrow pointer that shows you the actual direction to your next way point. You'll have to pay extra to buy city navigational maps to the 78 so I'd say skip that and just get a Nuvi for the city stuff. Plan on an additional RAM mount in your costs.
One of my favorite features of the Garmin 78 is auto track creation. Go for a nice ride and don't worry about keeping track of where you've been, the 78 will do that for you. You can download the track later and share it with your friends or upload it to the forum.
You can spend more money and get a fancy, waterproof GPS and that's fine, you'll just have to learn how to use one device then which is a plus. I ride with both a Nuvi and a 78 and enjoy the features each offers. When I'm on the highway, I configure my 78 to just show accurate speed, elevation and distance travelled.
Bottom line is these things are really cool and make life on the road or trail much easier.
;-) Paul