Knights north staffs (Stoke) is the one I use most. I do approx 30k a year in a privately funded car.
I find them hard work to be honest. Many of the staff have a veneer of extreme politeness, which I could do without if I was getting a more genuine response instead. That said, they seem to have stabilised with some much better service staff of late, Leanne in particular always seems to talk sense and be genuinely helpful.
Fastlane servicing always seems to take longer than expected. Free wifi, but you need to get a special code, which takes time for no real benefit. Starbucks coffee a nice touch.
Number one gripe though is when you arrive in a hurry to drop your car off on the way to work, you have to wait whilst they find you on their computer, mess with your key, print out about 10 separate sheets of paper, collect them from a shared printer behind them. All in all there is a good 15 mins worth of contact for something that should be as simple as swapping keys.
Holdcroft subaru by contrast have all this paperwork ready when you arrive. A quick swap of keys, a sign here and 3 mins later you are off again.
Over the years I've found them difficult on non-routine problems, such as broken headlight washers, door lock actuators etc where they have been keen to get me to agree to paying "investigation costs" despite being a very regular customer, and the issue being one that is known by BMW and therefore very very likely to be FOC. Doesn't seem necessary.
Perhaps I'm giving them a hard time. Certainly they are no worse than Bluebell Crewe (3 hrs for a standard 90min fastlane service).
Personal favourite was Bluebell Wilmslow who were always straightforward and easy to deal with, but I no-longer work near there!