Cheltenham often gets referred to as the stiffest track in the country but in truth it doesn't even come close.
Towester is much stiffer and one the layers like. Horses that look to be cantering 3 out can end up tailed off.
Kelso has a very stiff uphill finish much stiffer then Cheltenham and so does Carlisle.
The undulations and the changes in speed can exhaust horses and probably that's what make the Cheltenham Hill look stiffer.
Chepstow is another course with undulations and on soft/heavy ground horses are forever finishing legless there
Other course like Exeter Ascot Hexam Plumpton Sandown don't take many prisoners if they are lacking in stamina
Overall I think Towester is regarded as the stiffest track in the country.
Cheltenham's stiff inasmuch as the hill features twice in 2m races, and 3 times over 3m. Towcester's similar, Kelso isn't, as most of the rise is after the finish.
Fwiw, I've always considered the RyanAir distance less of a test (relatively) than the QMCC, as much of the extra half-mile of the former is downhill, (and I'm bored sh*tless ).