I'd say ethernet is the safest, although I must admit I'm not sure why. Did you watch The Real Hustle last week? The guys were able to sit outside in a van on a road and search for wireless connection users with components added to a laptop that they easily bought off the internet. They found 3 or 4 users where they could have hacked into the peoples computers. They concentrated on one and managed to hack into his computer and steal all his details (and I mean all). I think they said something about having to buy extra security if you do have a wireless connection.