I've been in the modding community before 2003, I built my first lovely map in 2004 and since then I've been designing various things. I'm a jack-of-all-trades, but a master of none. University arrived, and afterwards work 'n' stuff, so I didn't have much time, but now I found some spare time, compared to my daily routines and I've planned for a lengthy period for a certain project that I would like to work on. I'll be designing something of a Sandbox game, a small city with a surface of 30 km^2 and I was wondering which is the proper engine for such a thing? It will be intended for PC, since I've been gaming on the PC 90% of the time, and I would love to make this an open project, once I have something to show for it. I started off with GoldSrc, continued on to Source and they have severe limitations to their maps, making my project difficult to accomplish, so is there a suggestion as to what should I decide to use? I am hesitant between Unity3D and UDK. I'd love to hear your experiences and suggestions. Thank you.