FewCloudy Agreed with S5 and the west end in general - good fun!
S27/28/34 can be very busy. I find 28 always a bit stressful to get things climbed on headings and stream all the Liverpool / Manc inbounds, but good for speed control practice.
By contrast, S9 can be nice and relaxing - often on directs due to free route airspace and level separated - a case of giving a shortcut if possible and not much else.
TC wise, LAM can be good fun on its own: the stack seems to be the busiest for Heathrow, flows in all directions from Stansted, Luton and Heathrow outbound, plus Gatwick outbounds being climbed against all that and the Heathrow inbounds.
BNN also fun for the same reasons, while COWLY / WELIN can be fun combined. A bit like STAFA / TRENT, lots of traffic up, down and the odd bit of traffic to somewhere like Norwich that needs to cut across all the inbounds.
I don't know Scottish very well, but IOM sector always seems like there's stuff to do - headings for Manchester / LTMA inbounds, descent for Dublin traffic and climbs for everything else - even if it doesn't quite have the traffic of the London area, as well.
Have fun!