Virgin, without a doubt. Been with them since they were NTL must be what, 15 years now.
Will go in depth as to why, just to steer you away from SKY who I detest with a passion. Have family with them and they are shite. They hardly use the internet so were on the basic broadband pack. Had friend to stay for a couple weeks which sent them over their measly 2GB use (we use that in a day!) Sky increased their pack next month and said as they had gone over they HAD to upgrade. Family said to Sky what about the previous 12 months where they had hardly used a thing, does that not balance things out seeing as this extra month was a one off, Sky did not wanna know. Also their call centres cost a bomb on an 0845 number. Virgin is free, you just ring 150 from home phone and choose your option.
Never once had loss of tv service with Virgin, programmes never fail to record, can record 2 while watching a 3rd. With the V+box you can record 80 hours of stuff. They warn you if your set-to-records will clash.
Broadband is fast, and what it says it is. We are on 30mbps, soon to be doubled to 60 by August for free, new customers now go straight on 60mb package. Depending on how thick your walls are and how good your pc is. I get 30mbps wirelessly on one pc which is on a 2nd floor from the router, but on a 5 year old laptop on the same floor only get 22mbps. If you have a wired connection or get some Home Plugs (these give you a wired connection using your plug sockets) you will get the speeds they say you will.
You can change your phone package to suit,so go for an international call package to give cheaper calls, I am on the Talk Anytime so all landline UK calls are free, never phone abroad so not sure of that package.
Also am quite sure Virgin is cheaper (compare the long term costs, ignore any half price for 6 months etc when comparing both)