They all have at least 12 months and BT themselves are the cheapest out there with the best usage surprisingly.
AAISP's usage policy is a bit ridiculous for the standard £21 package. 2Gb for the entire month during day time?!
Pay your money take your choice, you can buy extra units anyway. They are not an ISP aimed at the every day consumer, which is good as it means their network isn't overcrowded by the sort of people who think that paying £10 a month for their internet connection should give them everything they ask for.
TBH I can't see how the average person (excluding houses populated with lazy students and folk who sit around all day on their arses downloading stuff) can get through that much data during daytime hours.
IME People generally massively over estimate how much data they actually transfer.
I work from home a lot and generally never manage to get through more than 6-8Gb a month during their peak hours. And around 80-100Gb offpeak, most of which is iPlayer traffic, the odd game from steam and a few big downloads.
Either way with 10Gb of peak use and 150Gb offpeak it wouldn't cost me much more than £40 a month which considering their service is beyond reproach (makes Zen and co look very very poor in comparison) I don't consider to be that bad.
Add into that services such as full DNS control, routed IPv6 and as many real IPv4 addresses as you ask for it starts to become very good value in my eyes.
You do also get the advantage of a 1 month contract and units roll over too, so you probably find you need less than you think.
Sure they're not as cheap as BT but they are not generally interested in the same sort of market, they are a business focussed ISP mostly and their tariffs reflect that.
