I have been a TalkTalk Business customer for some time. I originally subscribed to Freedom2Surf (F2S) ADSL Broadband back in 2004 and was migrated to TalkTalk Business when F2S was taken over and have been with them ever since.
I recently upgraded from ADSL to the Fibre Complete package and also transferred my line rental and telephony package at the same time. The overall cost is comparable to what I was previously paying for broadband, line rental and calls.
My house is right next to the cabinet (estimated line length <100m) and I achieve ~74mbit download and ~19mbit upload speeds as reported by speedtest.net, which I assume is as good as it gets.
In all the years I've been with them, I can probably count on one hand the number of times I've had issues. I had an ADSL modem die after a lightning strike around 10 years ago (not their fault), and once service died for 24-48h due to equipment failure at the local exchange, so I've not really had much occasion to contact their customer support. The service has otherwise (touch wood) been very reliable with excellent uptime.
For me there were a couple factors that massively influenced my decision who to take a fibre package from:
1. I run a server from home so needed a fixed IP address (Fibre Complete gives me 4 fixed IPs) with no blocked services.
2. I see absolutely no point having a fast package with usage limits, so I wanted an unlimited package.
After I purchased my upgrade to fibre I had to converse with their support dept to update the rDNS on my IP, which after a few emails back and forth their DNS dept was able to resolve for me. It took a couple days to sort out as they confirmed my identity and gathered the necessary information from me, but I always felt like the situation was progressing and they knew what I was requesting and what they were doing. Overall I was satisfied with the service as I had not expected that particular task to necessarily be straightforward.
TalkTalk Business are currently supplying a Huawei HG635 SuperRouter which should be OK for most home/small office users. It seems stable and fast in my experience and the wireless is more than adequate. It handles port forwarding. My only gripe was the firewall, which although adequate for most SOHO users did not give me the flexibility I was looking for so I chose to add a separate firewall box to my setup.
If you have any specific questions regarding the service, please feel free to ask and I'll be happy to share anything I know.