Are you talking about within Manacube, or just vanilla Minecraft itself? Because I would have different answers.
Manacube:
Probably creative. I've just started to explore Manacube's creative server, and I'm loving it a lot! I have a lot of good friends from survival, but the gamemode doesn't interest me too much.
Vanilla:
Survival definitely. I'm not too good of a builder, and survival is how I started off, and so I'll always go back to that.