I've also looked at many of these, and for the RT, THIS is the one I prefer. It's from Rivco, who is also a site sponsor.
The bracket is made specifically for the RT. I like it because it eliminates the need to install a clamp around your handlebar. The cup holder (sold separately from the bracket) comes in chrome, black. or leather, and includes various size foam inserts to handle any size cup. It's very well made - all metal, no plastic, yet it isn't terribly expensive.
Here is a picture of the chrome one mounted on my Spyder.
The Drink-2-go one, mentioned by James68 above, is great for the rear seat, as it will clamp securely onto the rear hand grip.
Congratulations on your new RT. There's lots of fun in your future. :thumbup: