Dartmoor kills the Q’s and Exmoor if you know where to go.
I reckon it depends on your riding preference – if you like escaping, feeling way out of it and don’t mind slogging up/along some tough terrain to get to the best bits and best views, it’s got to be Dartmoor. The surefire bet on Dartmoor is the MBR infamous kilelr loop around manaton etc, but i prefer to get a bit further off the beaten track personally (less ramblers to clash with!).
If you want non-stop trails that you can blast almost all of, followed by a gallon of rough cider – it’s the Q’s (but please do remember – as the guys above say, thats Zummerzet).
Exmoor’s ok, but limited comparitively.
Cornwall – is a tricky one! I don’t know of any great spots. No doubt you could hack Bodmin moor, or be cheeky and ride some of the nice coastal paths – but other than that, no idea where you could even start!
Someone must know – Camel trail?! lol.