In my experience, the RP1000 (and its smaller brothers such as the RP500) is easy to tweak, due to fairly shallow menu options, and still sound really good.
The GT10 has a lot more options to play with however, and if you're willing to read through the manual you will get the sounds you want out of it.
If you ever decide to get the RP1000 feel free to PM me for tips on setting it up