Thomas the Tank Engine

Iain loves Thomas the Tank Engine (I'm obsessed with Tomas and any and all trains). When we went to see Brian at Fort Sill in OK, Brian got Iain his first Thomas train wooden play set. And since then he has gotten 2 more trains, aquarium cars, and and expansion tracks for the wooden play set and he even has a battery operated train (which is pretty cool). Brian asked me to pick up a big Thomas wooden train set (which I have yet to get. I will hopefully on Monday). But which one to get? Any suggestions?