No idea. I use mainly Debian but I think Ubuntu has a more aggressive update policy and is based on Debian. Not sure about RH since I don't know a lot about their package managers. But CentOS and Fedora are probably also quite up to date.
Oh Ubuntu is like Debian to me... in fact when I was taking about Debian this whole time I was actually talking about Ubuntu. Its latexmk is the one that's old.