The problem with these figures is that the complaints per 100,000 don't tell us if those are related to the actual customer service, reliability, speed, latency, billing process, price hikes, etc.
Furthermore, these aren't just moans. They are cases when the problem has not been sorted by the provider to the customer's satisfaction, and has ended up at OFCOM.
For example, Sky has a historically low rate. This might mean that the service is good and that they are good at fixing problems. But it could also be that they are happy to release unhappy customers from their contracts, or offer them compensation to settle the dispute.
Perhaps you are right. Also, it could be because they have customer service based in the UK.
Their router is also of better quality. I noticed that Now Broadband have a router with only 2 Ethernet ports! That is also a major minus point that can affect their ratings. Even though people can use a network switch but it is something that most people would not want to have to deal with.
Also TalkTalk have a customer base in India and also in South Africa if I am not mistaken. Many people have complained that when they contact customer service the people in Indian call centres are not able to resolve their disputes or are not aware of outages that have happened in their area in the UK.
This can be a big problem when you have to deal with customer service overseas especially with people who don't speak English clearly. Sometimes it is not easy to recognise Indian accents and that can also be annoying when you are on the phone. I've seen these rant videos on youtube regarding TalkTalk. Some customers have had difficulty cancelling their service as they kept getting billed even though they are no longer with TalkTalk.
However, it is important to mention that there are problems that some users experience particularly in ADSL Exchange Only Lines where regardless of what ISP they choose on the Openreach network, these problems cannot be resolved!
I was on EO Line until Oct 2019 and my connection drop outs could never be fully resolved. I was an ADSL customer with Tiscali, Sky, Be Unlimited and Plusnet and before that back in the early 2000 had Dial-Up, which had even worse drop-outs every 2 hours.
No engineer could help me solve those problems at that time. Yes, Sky were quite prompt to send their Sky engineer in our flat to have a look at our line. I remember the engineer said he could not find any line fault in our property.
The only way that solved the problem partially was to raise the noise margin profile from 3dB to 9dB and only then the drop outs stopped! But this meant that the speed was slightly reduced from 16Mbps to 12Mbps. But even then some mornings I would see the noise margin drop from 9dB to below 3dB and the connection speed dropped drastically as a result before recovering back. Connection would slow to a crawl, below 1Mbps before recovering back to 12Mbps and this was my observation with the noise margins.
Every switch to a new ISP meant that I had to inform my ISP to manually raise my noise margin dB. This was one reason why I remained a Sky customer for 4 years as I didn't want the hassle of informing my new ISP to make this change. But I only finally left Sky when their price were hiked too high.
Only FTTC solved my problems permanently! It could also be that a few unhappy customers out of the 100,000 are still on bad ADSL lines or their FTTC cabinet is very far away from their property.
I think when FTTP becomes fully available and ADSL/FTTC retires for good in future some of those complaints will be reduced as customers will naturally not have to deal with these problems any more.
The problem with these figures is that the complaints per 100,000 don't tell us if those are related to the actual customer service, reliability, speed, latency, billing process, price hikes, etc.
That's as far as i got.
As i said I have been with TT 15+ years and have had great service you have told us you have used both and prefer BT well good for you, time to move along i think 
Indeed, if you are happy as a TT customer for 15+ years then that's great for you! But do bear in mind that you are overpaying for your service unless you are able to haggle with their customer service to keep your prices lower! For this reason you might want to consider your options.
Also, if you haven't tried other ISPs in those 15 years then you won't be able to compare your service to your existing TalkTalk provider. How will you know if your service is really the best you are getting? Even if you are happy with it!
For example, incidentally last night I had a drop in my connection after 173 days uptime! However, I knew this is unlikely to have been BT being unstable. This happened at around 2:30am so I knew this was a firmware upgrade!
Firmware version:
v0.44.00.04123-BT
Firmware updated:
8-Jan-2025
I checked the firmware and it has been updated to 8 of January. I always check this and at least this isn't a technical fault with the service or the router. It was a router reboot to upgrade the firmware of the BT Smart Hub 2 router.
I can confirm that from my checking with TalkTalk those connection problems were not related to firmware upgrades. Maybe you were fortunate to never have suffered from these problems. But I always had them every few weeks when I was with TalkTalk.
I guess my only complaint I would say that I have with BT and that goes with any other ISP is that the ISP supplied router firmware update cannot be disabled manually! If I had my own router I could disable automatic update. I don't have that option in the router settings. But other than this issue I have no other complaints with the actual service. It would've been great if at least ISPs informed us when they'll be pushing an upgrade for their routers.