You should get the same speed from all ISPs as your exchange is "Up to 8 Meg" IPStream only, other than exchange congestion, which is unlikely as it is a small exchange, or ISP core network congestion.
There is no point in being with AOL there as they have no LLU.
Have a look at BT themselves, Plusnet and EE.
Do you have your phone with BT? Do you want to keep it that way?
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC