I'd say survival mode... with creative mode it removes that feeling of panic when you're playing... because, you don't have anything to lose and dying becomes nothing. But in survival mode you're on the edge and you have to watch out for any creepers and stuff like that lol. Though after a while it does get frustrating.
So I guess it all depends on what you're gonna play minecraft for. Have two separate worlds - one for survival and one for creative. Use the creative mode to just build stuff you'd take forever to build in survival, and play with your friends in survival mode :D