Yes Penzance would not be a good choice. A reasonable compromise would be Okehamption in north Devon just on the northern edge of Dartmoor. Cornwall is actually pretty long and you don't want to be at the very end, which Penzance is close to being.
Some of the very best pubs in the UK are in the "West County". Get the latest copy of the Good Pub Guide and study it (really). www.thegoodpubguide.co.uk
I would drive. Having said that you need to be a confident driver in the narrow lanes of Devon and Cornwall. BUT it IS a great part of England. You MUST get off the major roads to really see it.
Also, don't miss Glastonbury in Somerset. I love that place-it is very special.
BTW, Devon (especially north Devon) is probably the most "quaint" part of England. WAY better than the Cotswolds. You are likely to run into far fewer tourists there too. In my four trips there, I don't think I ran into one American. Devon is fabulous walking territory too.