I had BT Vision for a couple of years and was happy eith it. BT Vision downlods do not count towards your download limit.
To be honest the only reason I changed to Sky was financial, I recall that my monthly costs are about £20 a month less than I was paying BT.
I transferred everything to Sky including line rental, it was quick and painless with no service interruption.
BUT my loyalty is to the supplier with the best deals so Virgin media are on my list to investigate once my Sky contract expires in january.