I was with FreeServe/Wanadoo pay as you go dial up for about 4 years with absolutley no probs apart from a really slow connection from time to time. Switched over to their 2Mb broad band service 10 months ago and haven't looked back. I'm using a modem + wireless router + printer server thingy, which slows things down a little bit, but is worth it for the freedom it gives you with the laptop.
My daughter uses the internet a lot, but we've never reached our traffric ceiling. If you intend to download videos or plug your playstation into the internet then you probably want a no limit service, which starts to make Wanadoo a bit more expensive and less competative.
"Which" Magazine rated Wanadoo's support as being poor, but I've never had to use it so I can't comment. The fact that I've never had to use it must be a good thing though.