I'd say none of the above. Go to Italy, primarily Tuscany, Bologna, and Campania. It'll be way more relaxing, cheaper, and the food is less disgusting (e.g. tartar, foie gras, etc) than mainstay Parisian French food (with the exception of Allemagne-style french or french vietnamese).
My personal favorite place is Sorrento in Campania, but the food in Tuscany is beyond belief, and you can rent a car and spend the day driving around Chianti sampling wine, olives, vinegar, fresh Cheese and Proscuitto, at various middle ages style city-forts, and then take in some real Tuscan dishes (especially the soups) at local mom and pop restaurants.
Although, if I had to choose between the three, I'd to to Switzerland. I find Paris and London too stressful, more of a "vacation of work". That is, going to all the museums and stuff is just alot of stress and walking, I find I'm on a schedule "oh, must finish Louvre in 2 days, then go X, then Y, etc"