In Paris, my 14 year old son's favorites are FS George V, and the Peninsula. He really liked Le Bristol, Park Hyatt Vendome, and also Plaza Athenee but the first two are his favorites. FS George V has an awesome pool and fitness center, and F&B is excellent. Peninsula also has an awesome pool, excellent F&B, and views of the Eiffel tower from L'Oiseau Blanc and Le Rooftop are pretty special.

In London, his favorite is the Corinthia. The swimming pool, vitality pool, and amphitheater sauna are hard to beat. F&B across Kerridge's, The Northhall, etc. was excellent. Location is a block from Thames, and easy walk to Trafalgar, Piccadilly, Covent Garden, Regent and Bond Streets, etc. Our Executive room faced the street, was very quiet and we didn't have any wifi issues. Ham Yard was also a big hit... great high energy hotel and location... and the bowling alley is a really fun amenity.

So many great choices in Paris and London :-)