Conducted many enjoyable flights from Exeter and for me the best bits are
Down the Exe estuary to Exmouth and along the coast to Slapton Sands and the estuary to Salcombe, pass by Dartmouth naval college on the dart.
Return via Exmouth low level along the coast and estuary (keeping emergency options in range)
If you can get to North coast as well then even better
Dartmoor is great but weather can be unpredictable and dodgy !
Enjoy !!