Train travel

Angie, What do you mean by best? Most people mean quickest. Or do you mean most scenic? What method of transport (car, train, other)?
Do you want to do this in one day, or stop off overnight?

For quickest, by car use one of the route planning sites, for example: https://www.viamichelin.com/
By train, use one of the rail company websites, for example DB: https://www.bahn.de/p/view/index.shtml This will always find you the quickest route.

If you're travelling by train, it's not as if you've got a lot of choice in routes. Looking at the SNCF website, all trains require 2 train changes, in Ventimiglia and Genoa. Unless, of course you want to take deliberate detours to other stops, which would require booking separate tickets.