I would recommend quagga as the best maintained, but I'm one of the
maintainers so I am biased.  The quagga fork happened in part because
obviously correct bug fixes were not getting into the zebra tree.

http://www.quagga.net/

See pkgsrc-wip/quagga-devel, too, but beware that /var/run/zebra
disappears on boot and I haven't fixed this yet.  But a lot of other
stuff is fixed over 0.96.4.

quagga has had some instability lately, but is now in pretty good
shape.

It is currently undergoing conformance testing at UNH IOL for OSPF.

I run quagga with ripngd, ospf, and bgp (the latter for my 6bone feed,
over v6 with v6 prefixes) (on netbsd/i386 mostly with the main router
(w/ bgp) on netbsd/sparc64.  I have not tried v4 bgp, but people seem
to be using it successfully.

gated is either very crufty or nonfree or both.

I have heard people claim that mrtd is unmaintained.

-- 
        Greg Troxel <gdt@ir.bbn.com>