O2 Data network's crap anyway
And their call isn't much better, just left their simplicity pre-pay after just a month - even loosing £17 worth of credit as it was just that poor. Was on t-mobile before it and Vodafone now and they're both far better in call and data.
At least by my anecdotal, small area sample set.
Don't know much about Orange, had a bad experience with them a few years back and not going to touch them, one of the reasons I've left t-mobile too.
O2 used to have a decent network back when I had a contract phone with them, but then that was before iphones too which have probably saturated the network - either than or pay as you go customers just get a dialed down shitter service, which is possible as they have different settings to contract customers for data connections (who also have different settings to iphone users) so they should be able to tailor the service based on customer profile.