If WiFi is a must then BT is better than Orange but you're still at the wrong end of a long straw with both. PlusNet, Zen Internet, IDNet, Eclipse Internet and others should be considered too. Granted WiFi is going to be a bit out of the window with them but it really depends upon what you want and how much you're willing to pay.
Also remember that even the best ISPs can have problems, any move will carry some risk.
Separate from that I would say the BT Infinity service is still quite good if you pick their "unlimited" package but obviously you can't get that one so..
Mark 'Winter' Jackson
Editor-in-Chief - ISPreview.co.uk