To add a bit to this beauty pageant of sorts: I'm most definitely set on using the Transvoxel algorithm as the game is set in England. It's of utmost importance to convey the topography of the country with its hills, valleys, etc. Which puts me in a corner, of sorts. I hear the C4 engine bodes well for all intents and purposes; the question remains, would it support the dynamics of location based programming and multiplayer network physics that I envision?
Unity 3D comes with a price-tag, but If the benefits outweigh the costs, it's def. worth it; unfortunately, C4 is not particularly fitted for mobile development, or perhaps i've misread the guidelines.