definatly wifi becouse i'm not always close to friends who have an iphone/touch and also becouse of openfeint and stuff like that x)
We use bluetooth to play games here at work during lunch, while waiting for meetings to start, etc. Favorites include Flight Control and F.A.S.T. Sometimes we crowd around one device and play SlotZ Racer...
Check out my blog for some technical details on both: http://volcore.limbicsoft.com To summarize: Bluetooth is nice for it's ad-hoc capabilities, but if you want reliability, throughput and more than 3 clients there is no way around WiFi :-(
bluetooth, if i can only use wifi to play online, i'll rather play on xbox live, but with bluetooth i can play all my mates at college which is more fun to me, Real Racing and A4E!
1st gen touch here too, so WiFi. But even if I had the option I'd still vote for WiFi. Why? Because WiFi isn't only for multiplayer, obviously. Push notification, uploading scores globally, etc. all raise the level of importance in putting WiFi support in game. World-wide multiplayer is icing on that cake.