Good question. I guess it will depend a bit on what kind of a game you want to develop, i.e. if e.g. the complete landscape will be visible all the time or if you have more of a "jump and run" and the landscape is continuously generated.
In Qubicle you can influence some parameters during the design of landscape. You could create 3 different versions... 1) mountain, 2) flatlands, 3) hills... and use the 3rd one to link 1) and 2). However, you will have to adjust the intersection manually, to have a real smooth transition.