I've used NFPS/Rocket/IKS66, and it sucks. Bad service, constant buffering, missing channels, and a guide that never works.
I've used IPguys. It's overrated, outsources international channels to other (bad) providers, also has buffering issues, and has no UK channels.
I'm disenfranchised. I don't know which service is worth signing up for.
FabIPTV is your Huckleberry. Excellent UK selection, almost perfect video quality and rarely any buffering for me. Message /u/fabiptv here for details or a trial.
Flawless, through reseller /u/maniac1000, would be my second choice if you want a larger selection of VOD and the option for SD feeds if you have a slower connection.