I have virgin media and have never had a problem with it, but we get TV with that too

Tesco do a few different packages depending on what you want.

I've never had any trouble with them and they've always delivered what they said they would.

A friend of mine who lives and travels in some very poor signal areas has recently signed up to T Mobile broadband for use when she is on her boat. In her experience T Mobile have provided the best coverage of any of the providers she has tried in the past. I also use T Mobile for my phone an apart from one isolated instance in the Isle of Wight recently have been very satisfied with coverage.

Is this for a mobile phone or for the internet?

3Mobile is the only one, that provides Mobile Broadband on a Pay As You Go package, AFAIK. Their are package prices are reasonable, based on monthly usage allocations.

If there's only a few quid in it, go for the service that provides the best coverage in your area. There's nothing worse than slow and patchy internet coverage when you're trying to answer one of my questions..;-)