Also depends on your use of p2p and of upload. If you use p2p a lot, BT (for who I have just opted) appear to be useless. If you want higher upload speeds, Sky will charge £30 per month, if they offer the service at all (they don't for me). My BT upload speed should be 19Mb, Sky could not offer better than 2Mb here.
Happy BE user for several years