Looking at ride reports here on Advrider gives one a pretty decent idea of what is possible where.
It is also worth looking at Google Maps and turning on Pictures to see the general scenery. Also... the more pics in the area, the more touristy it tends to be.
I heard good things from Sri Lanka... but only from Sri Lankans. When I tried to point some more specific questions about Sri Lanka to them, I didn't really get much insight. It seems like it a very over crowded country (850 people per square mile) that is probably as dirty as India and the scenery doesn't look all that special... But I don't really know, I've never been there, I'm just guessing.
If you are familiar with India, you must do Leh when you have 2-3 weeks to spare. Delhi has cheap direct flights, and Leh has increasingly more motorcycle rental places (rent something other than the cheap, old Enfields, though.) You will not only enjoy riding there, but you will be itching to go back. Guaranteed.