I am planning to go to the beach from Paris for 3-4 nights and then return to UK. Which one of these beaches is a better destination for a hot summer holiday?
None of these are particularly hot. Deauville is fancy and expensive, De Panne much less so, the beach is wilder, but colder there. Deauville is much easier to get to.
But if you want warmer water and air temperatures without straying too far from Paris, you should head west to the Atlantic. The La Baule and Les Sables d'Olonne areas are easy to reach from Paris.
The seaside resorts in Belgium with all their appartment blocks are not so attractive, however I would go to De Haan instead of De Panne or what is more comparable with Deauville “Het Zoute” in Knokke close to the Dutch border if you don’t mind the presence of the harbour area of nearby Zeebrugge. Speaking for myself my preference in France would be La Baule, very pleasant laid-back atmosphere and a bit posh but not so much as Deauville. To my opinion one of the best places along the French Atlantic coast.