Rich,
Can't comment on the price part of your question but our works mobile broadband are Voda (and they pay
) and I don't have any problems with it quality wise. I don't know if it means anything but our modems are the PCMCIA one and not the USB dongle.
Strong 3G signal in most of the big towns/cities I've been to and consistent with reasonable data exchange rates (but slower) 2G in some of the not so big towns. The 2G is good for most work things (like email) but surfing the net does show you just how slow it can be sometimes (think back to 56K dial-up).
Only once had a problem of no connection somewhere in Cumbria with no Voda coverage at all (works phone included) and only 1 blob on my T-Mobile phone so it was more than likely the area. Basically, check where you are likely to use it on a coverage map.
At home I am right on the cusp of a 2G/3G network and if I log onto the system whilst in a 3G bit (like by the patio doors) it hangs onto it when I move around the house then.
Judging by what I have used, if I need to get mobile broadband I'll probably get the Voda option.
Hope that helps.
Ian