I use Andrews & Arnold. I've used Zen briefly as a trial too. Talk to aa.net.uk about their Home::1 deal. They aren't the cheapest but there's a good reason for that, as they really care anout 100% full speed and everyone you talk to knows more about it than you do, a refreshing difference. It doesnt matter what you level of expertise, they seem just dedicated to getting things sorted out properly, with no fuss. As for kit, you can choose and use your own, or use their excellent, tested recommended kit it doesn't matter.
Take a look at ispreview, anyway. Lots of other posters on here have their own favourites such as Zen. Surprisingly a lot of regular posters on kitz use ISPs yet keep complaining about problems with them, Plusnet for example, picked out at random quite unfairly as there are plenty of others.