Switched from Plusnet to TalkTalk Business a few weeks ago on a special Black Friday offer after reading some good reviews from people as it is a very different service from the retail arm. The likes of A&A, idnet, Pulse8 & Uno use TTB for some of there services.
So far I am very happy, my upload speeds have increased by 2-3 Mbps and upload has doubled, seeing less errors and better latency. Not yet had to use support but understand its good and UK based.
I chose the Complete with Fibre package which has Unlimited UK landline and mobile calls and several call features included. I was a little worries by the 24 month contract but they will let you leave penalty free under the OFCOM Business Broadband Code of Practice if they cannot resolve any issue within 28 days, even if you are in mid-contract.