[Parhelion]

I take it you want to use a different one from the one you used with Transgenesis because the overall gameplay is going to need to be different... but without knowing what that gameplay is, we've got nothing to go on as far as suggesting new codebases for you to try out.

This is something that you might want to discuss with your current staff, especially if any of them have any experience with other codebases. I also suggest that you figure out precisely WHY you want to use another codebase -- exactly what features do you want changed and how? Is this functionality going to be something that already exists in another codebase, or is it something you are going to have to write on your own? If it's something you are going to have to write on your own, wouldn't you prefer a "lighter" (less developed) codebase, as opposed to one where you end up wasting a lot of time tearing stuff out?

I do commend you having already done test runs for your games, though.