Darren,
Flying lessons, and here is why I think so. I used to use a sim, before I started my lessons, and it taught me to fly using instruments, not visually. If you become proficient on the sim, you may learn some bad habits for when you first start flying. Firstly, there is very little incentive for using co-ordinated rudder when turning a sim, whereas I find the withering sarcasm of my instructor means I have to pay close attention to the little ball. Secondly, and probably more importantly, I found that flying the sim, I would make extensive use of the Artificial Horizon (AI), whereas in the Warrior I glance at it only as a reference to bank angle during turns. At all other times I have to fly with reference to the visual horizon.
I agree with Slasher, sims are great for practicing IFR flight (something I can only aspire to) but for VFR, there is nothing like the real thing.