Could you tell me please where and which is the best download for Handbrake?
That depends on the OS that you are using, for windows the 64bit would be the best bet.
Handbrake.fr is the way to go, indeed.
Unfortunately, the nightly builds are indefinitely halted unless you are using Ubuntu. I believe the mirror server hack is responsible for that. Last released compiled Windows x64 nightly from Handbrake.fr was dated May 2, 2017.
Yay! I missed it but the Handbrake snapshots are back for Windows & Mac. Not nightly builds but at least we can grab snapshots!
Note: To be honest the Windows & Mac may always have been snapshots. I never looked closely enough. Still nicer than simply being stuck with the standard official stable releases.