...O2 were selling the iphone4Gs upgrade at the SAME cost of the iphone5 upgrade, so I guess apple are in some ways not differenciating too much, although could be reverse phycology fooling people into buying 4gs stock because of few 5s available...
So assuming you could get your hands on one I'd be second to recommend iph5, for me:
iPh5 cons - lightning connector 30pin change - need to get adaptor for my 3 existing dock appliances, O2 nano sim activation took 3 days elasped time,
iPh5 pros - speed of operation compared to iph3 was night/day, all existing apps work including TomTom app, supposed no antenna issues / better reception, 8MB camera is good (using the doc scanner app today very useful), supposed 4G ready (when it comes out)
My other half has a 4g and it compares well, except for the 5MB camera...