However, having had flawless service from O2 for years then having a bad patch with Sky I'm cautious that the mass market ISPs are great when things work but can be next to useless when they don't.
Same with BT. I moved from BE to BT Infinity 2 and mine has been flawless, but if it broke I'd be using the twitter team rather than the helpdesk.
I would suggest plusnet, as I'm slowing coming round to that being my next ISP, they're cheaper than BT and have changed radically since being acquired by BT.
AAISP is a very good ISP but don't underestimate the usage you will use on a higher speed connection. I find myself using 140GB a month on average on fibre 48meg, but on BE (14meg) I would use probably 40GB a month. AAISP would be very expensive for me, even on their Home::1 plan. (shame as I like ISPs with 'clue').
James BT Infinity 2
19/09/2012 - Sold 42/6 - Getting 49/8.5 - Sync 53 / 9.5 Mbps @ 470m approx
14 years of broadband (ntl: cable to BT FTTC) - Router: Asus RT-N66U - Modem: Huawei HG612 speedtest