The "best" attractions is a matter of opinion and will depend on your interests. If you hate art, the Louvre probably won't be on your list of "best."

What are your interests? Famous sites, like the Colusseum and the Eiffel Tower? Historical sites? Museums? Are you interested in self-guided walking tours, or do you prefer guided tours? Do you plan on renting a car or using public transportation? More information is needed before you'll get helpful answers.

I enjoy famous and historical sights, I would love to go to the Louvre and I enjoy guided tours. I would probably use public transportation and trains.

For this kind of "best of list" all you need is a guidebook. They all have "best of lists" right up front.

Is there any other travel advice any of you have?

Why Toulouse? It doesn't really fit up with the others in terms of magnificence.

Cut back on cities, less is more.

Toulouse is of family significance and what cities would you get rid of for a first time europe trip?

I would drop Amsterdam as the outlier - land in paris and head south,. I would also question Toulouse - do you know exactly what you will do there and hot long it will take?

Six cities spread out all over the continent in 3 weeks is not going to give you much time to see anything but the surface. And since you haven't given us any context other than you like famous and historical stuff, which is in every teeny little corner of Europe, not much to go on.