Europe’s top tourist destinations in order are Paris, France; Rome, Italy; and London, UK.
Each of those top destinations deserves a fully dedicated trip for exploration; a few days will not suffice. Only spending a few days in Paris will serve merely as a tease.
London is approximately a 1 hour flight from Paris and Paris is a 2-hour flight from Rome.
A smart travel tip would be to visit the 3 cities in one trip. Hotels in Paris, Rome and London can be outrageously expensive so it is important that you plan for the right season to get the best deals. Another option is to rent short term rental apartments in Paris, vacation apartments in Rome or a fully furnished apartment in London.

Paris Art Photography by Laurent Harari