There are hundreds of them, and I don't much want to read more than one.
What's your favourite?
What's the most accessible?
What's the most authoritative?
What's considered to be the "classic"?
What's the most controversial?
I would recommend this one: http://www.amazon.co.uk/Napoleon-Alan-Forrest/dp/184916410X Written by this Historian https://pure.york.ac.uk/portal/en/researchers/alan-iain-forrest%28899d338f-caa9-4985-8208-d24bc4c66c75%29/publications.html
I'd recommend you look at this post.