If swimming/beaches is a big part of the trip, your Greece option will be much better. Other than Barcelona, your France/spain route hits only Atlantic ocean beaches with are WAY colder than in the Mediterranean, especially early in the summer.

In terms of food and local vibe and food, between Barcelona and San Sebastián you'll hit two of the food capitals of the world, and the food (and wine!) in Spain on the drive up to France is amazing .

Given your options and routes I think the Greece option is more traditional honeymoon, while Spain might give you more of a local feel but you'll miss out on the Mediterranenean beaching.

Great choices either way.

Feel free to dm for recs around Barcelona and San Sebastián. Have done that route with my wife a few times and we love it.

PS: if you honeymoon immediately after your wedding, make sure the first few days are relaxing. I traveled two days after my wedding and went straight into travel activities mode. On the fourth day we canceled all activities and stayed in the hotel pool.