I use plusnet although they are now owned by BT i think so probably comes from the same network. At the end of the day it all goes down a BT line unless you are on cable.

Is there a reason for changing your current ISP other than lagging? No matter what ISP you still might get the lagging and also other migration problems. Ideally you want cable, go to Virgins website and punch your postcode in and see if you can get it. If you can't, stay with who you with would be me advice.