Goa is better in terms of beach tourism .For safe uncrowded beaches I would opt for South Goa - Cavelossim or Benaulim would be perfect.The difference between Goa and Kerala is In Goa you can go for swimming/sunbat hing on all beaches, in Kerala there are a lots of fishermen beaches where it is not advisable to lay down and have a sunbath
Kerala is the home for diversed art form.Kerala is named as one of the ‘Ten Paradises of the World’ and ‘Fifty Places of a Lifetime’ by the National Geographic Traveler Magazine. so it is your choice now.

Kerala.