All three (plus BT and EE) were mentioned on BBC's 'Watchdog' last week.
Sky came out on top as the best of them.
My advice, if ever asked, is to choose their ISP based upon their after-sales service.
In most cases, it doesn't matter which ISP you use, their services get delivered down the same pair of high-end mega-twisted copper wires ... sometimes over our much-vaunted silver-copper wires ... which is where the highest percentage of a fault developing, exists.
Ergo, if you have an ISP that is good in this particular area ... the better IMO.