I find that Funtoo is more stable than Gentoo and there is a big advantage in getting a debian-sources kernel that you can slim down yourself or set up the gentoo-sources, or other kernels.
Another reason why I prefer Funtoo is that there is more innovation than in Gentoo (more quickly), and there are some pretty cool features in Funtoo that Ge too don't have (more stage architectures, epro etc).
Also, git portage ftw.
There is the question of you prefer the community in Gentoo deciding, which takes a long time or a few people deciding who has the best interest of the users at heart.