I have been with vodafone for about 14 years now I think.
The area I live in has reasonable 3G coverage and it seems to be pretty good in London.
Their customer service has always been very good.
My criticism of them recently is a gaping whole in the tariffs ( between 250mins and 500mins has no tariff. I use about 350 so I have to pay for the 500

)
Have you considered getting one on ebay?
Prices will come down before too long.
My price plan is like £35 a month and is an 18 month commitment which costs me £630.
I recently bought myself a G1 on ebay (unlocked) for £170. When my contract ends I am looking to move to sim only, O2 simplicity for example is £19.50 a month and comes with an unlimited (fair use) web bolt on and 1000 mins and 800 texts or something. Best of all you only have a 30 day commitment to them.
So, 18 months @ £19.50 = £351
Cost of phone = £170
Total: 521.
That's £100 quid saved even with buying myself a phone and I can change carriers at the drop of a hat.
Don't think i will be going contract again to be honest.