Gardens at Giverny and the gardens at Versaille?

We went in midsummer when the perennials in Giverny were at their peak but the garden is in bloom from spring to fall. Check the website for the months that they are open.

We’ve gone late spring these past 2 years and believe best time to see gardens would be early May as everything will be in bloom

I guess it might depend on the type of flowers you like to see. My preference has always been autumn flowers. I went to both gardens in August and it was great because the summer flowers were still blooming and the autumn flowers were too. They were both spectacular. I have also been to Versailles in early June and both the spring and summer flowers were blooming so that was gorgeous. Of course both gardens are famous for other features than just flowers, Giverny for the water features and Versailles for the formal gardens that are mostly trees and hedges. Anytime from spring through autumn is nice.

I went to Giverny a few years ago just a few days before it closed for the year, and it was still a pretty wonderful sight. Lots of zinnias in amazing shades and combinations, cosmos, dahlias, etc. But I'd think the absolute best time would involve the waterlilies in bloom....

Versailles gardens are really not flower gardens but a series of fountains in little wooded copses. any time spring summer or fall is fine. Here was a visit we made a few years ago: There are some flowers but if you want great floral gardens there are many in Paris itself that are better.
https://janettravels.wordpress.com/2016/02/15/fountains-of-versailles-a-little-chaos/
We have been to Giverny in spring and fall, both were lovely. Went on the last day it was open this year, not the ideal time but there were still lots of flowers in bloom. I would think for bulb flowers, April would be ideal and for fall flowers September. There is a site on their website that discusses what flowers are in bloom at various times. They strive to keep it looking good during the time it is open. This was our May visit -- many bulb flowers were done and roses not in full bloom yet. but still wisteria.
https://janettravels.wordpress.com/2010/05/25/not-so-secret-garden-giverny/

Thank you everyone for your advice and experiences.