Hi Jack, I was in your position not long ago, at that time I was with Zen who were excellent, their customer service is second to none, provision almost faultless, only had one outage in the several years I was with and, even then, it was due to circumstances beyond their control but it was costing me and I had a low cap on download, I needed more than my cap and decided to ditch them in favour of my mobile dongle with a higher cap. Once the contract on mobile ran out I ditched that and went to Plusnet for cost. I have noticed the difference, speed seems lower and connection drops frequently, as I am not dependant on it it is not enough of an issue to scream and shout.
If you NEED a stable connection go to Zen, costs you more but they are truly professional, if for cost, especially with phone bundle, go to Plusnet but be prepared for glitches.
Hope this helps.