When I originally started to think about 'which ISP' to use myself, I invested in a current copy of an Internet users mag. Try to get the best one you can find. Essentially, apart from a list of suppliers, deals and general pricing levels, you should also get some insight into which of them are delivering properly and which are slipping up (customer service, etc.)
I eventually opted for Tiscali last year, and after some initial problems when switching from 56kbs to 0.5Mb broadband, I'm generally very happy with the service. Most of the problems tend to centre around Tiscali having to make constant upgrades to cope with increasing demand (note, they, like so many others, have to buy their broadband access wholesale from BT).
Go through the mag reports and readers input carefully. Tiscali were not the cheapest at the time but I trusted them to deliver properly and they have. At £40.00 a month it was far more expensive than the £25.00 offering from Pipex but I erred on the side of caution. Shortly afterwards, BT slashed their wholesale prices by about 25% and Tiscali did pass those savings on to me so I currently pay £30 pm. More wholesale discounts are on the way from BT but this time the savings may not be passed on to the end users.
In the future, if I want to go for faster speeds of 1Mb, I may opt out of Tiscali altogether and go direct with BT Openworld unless they resolve some network/marketing differences that make higher speeds available to other wholesale purchasers. Remember to compare deals carefully: some providers are giving very attractive offers on things like waiving connection charges, h/w, etc. You can save quite a bit, so you must not just look at the monthly cost but rather work out a 12 month running cost after deducting special offer amounts. Also, are you confident that your ISP will still be trading this time next year? The technical glitches are largely sorted out now , but in commercial terms it's pretty stormy at the moment.
One last thing, Pab. I've no idea whether you're going to be able to get high speed access in your area. A quick visit to the BT Openworld site should let you know by checking your area coverage. I hope you'll be in luck. Alternatively, cable [fibre] is an alternative to ADSL broadband [twisted copper pair]. Do you have any cable TV/telephone services from NTL, Telewest, etc, that might be available to you?