The further west you go in Cornwall the narrower the peninsular gets, this gives easy access to both the north coast and south. St Ives would be a good base for this, in fact from here, any part of west cornwall can be reached easily : The Lizard, Godrevy, Penzance, Lands end, Cape Cornwall, Sennen area are all great locations with awesome coastal scenery.

However, Exmoor/North Devon sounds interesting as I've never been there and would find it hard to choose between the two.