It's difficult to know how you define "best place"; you don't really define what that means to you.
I'll say that I've had great results using FBM; but I'm good at weeding out stupid people/comments and also I do a good job of describing my sale items and posting good pics. FBM is the modern version of CL sales; so they come with all the pros and cons of dealing with the general public.
There are also venue specific sites for boat sales also (boattrader.com for example), but they often cost money. If you don't want to pay for advertising your boat, these won't be a choice you'd like.
We also have a "for sale / WTB" section here on BITOG; please note our rules for that forum.