Most monthly data allowances are basically unlimited these days anyway.
It depends on the network. Some are more expensive than others. Some resell their spare capacity under a bargain marque (eg. Giff-Gaff for O2, and Smarty for Three).
EE is one of the more expensive ones, but they do have the advantage of being required to have the best coverage as part of the Emergency Services 4G network (which still hasn't properly been deployed).
It all depends on what you're prepared to pay for (or can negotiate with the retentions department).
My current contract was originally £12 for 8GB/month (lots of mistakes by EE in giving me rebates), but is now £15 for 40GB/month (after a loyalty rebate) having withdrawn the original deal. That's more than I'd ever normally use in a month by a factor of ten.
The more important thing is that they have good coverage in rural NW Wales where my parents now live.
