I always wake up early, my wife likes to sleep in. From personal experience and reading online it seems many attractions are best when you are there first thing in the morning. The Pantheon in Rome was empty at 8 am and a completely different experience than visiting with the throngs in the mid afternoon. Staying in a hotel within a block of the Pantheon meant I could walk over and come back to the hotel for breakfast wake up the wife. We are staying on Isle St. Louis in Paris next Spring and I'm assuming Notre Dame with be a similar experience? The only way I'll visit Versailles is if my wife agrees to get an early train to arrive when they open. The weather is always cooler in the A.M. and most folks don't show up early based on what I've read on this forum.
Where else have you been that's better first thing in the A.M.?