UK: Carphone Warehouse vs O2 Store for iPhone purchase?

OK. Sorry for another iPhone related question but I’m taking the plunge tomorrow, and I want to know why I should / shouldn’t go for either of these retailers. I’m yet to phone round to find out stock, but the nearest store to work is a Carphone Warehouse.

Something irks me about them, and I worry that I wouldn’t get the same level of service as buying direct from O2 – would they spam me about phone upgrades or deals after they have my details? Did you buy your iPhone from CW and did they give you any reason to think O2 might have been a better choice?

For bonus points, recommend me some (prefereably free) app store apps!