Should I get a Nokia lumia or a

iPhone 3GS it's realy hard, spec wise the lumia beats the 3GS Hands down! But I have a iPad and have owned 2 iPod touches so I'm well used to the IOS software and love iCloud. I have also spent over £100 on apps and I would to have to buy more again! The lumia is an amazing phone, for some it's in the same legue as the 4s I also have to keep the phone on a contract for 2 years so I'm woried that the 3GS is not future proof. The lumia has a better contract with unlimited Internet were the iPhone has 1gb.
The lumia will possibly support tethering in the future but the iPhones network wont let you theather, it's not a big thing but it would be nice to be able to do it with the iPad.
I'm confused!

HELP!!!