Ok, Well I dont know why you would not go for 3?? I have been with them for years and had no hassle and remember they run off to O2 signal.
I use to sell Mobiles for a High street company.
Avoid buying from Phones4U, Car Phone Warehouse as they run on a heavy commision structure and try and sell you the worst deal for you and the best for them so they make the best commision.
If you want to go with orange then go to a Orange store and thats the same with all the net works as they have can slightly better deals then other stores, reason being they have to pay commision to other chains so like to try to put there saving a bit towards the customer, for example voda would pay Phones4u as much as �200 for 1 Contract, its a Big business so other chains would rather you went with them and took out there insurance as they make alot of money out of it.
Best Network depending on where you live is prob. Orange and there Insurance is amazing and is a must have.
Hope this helps