the man page for RADVD says:
radvd is the router advertisement daemon for IPv6. It listens to router solicitations and sends router advertisements as described in "Neighbor Discovery for IP Version 6 (IPv6)" (RFC 2461). With these advertise- ments hosts can automatically configure their addresses and some other parameters. They also can choose a default router based on these adver- tisements.
But there is nothing I see in man radvd.conf that answers how hosts choose a default router, nor can I find anything else about this.
Anyone know the answer or where to get the information???