Cities XL, the newest version, is pretty good once you get a ton of mods in it. Might I say its better than SC4, if you get the mods versus a modded SC4. The only flaw keeping it from being great is its lack of ram usage, quad core support, and it also has a crippling memory leak once you get a large city which lags PC's that are even new. I have a GTX770 which I modded by 26%, and even then, it lags because of the leak.
But I find myself going back to SC4. It is so dam addicting. Its so easy to lose many hours on it and not even realize. "Shit, its 4 am" type of game. Plus, how many city builders can you built a reactor for fun and set it on fire. Not many.