When setting XSESSION in /etc/rc.conf (as documented) it is not exported to the users environments, causing the vairable to be virtually useless, at least from console -> startx
Should be fixed in the latest "chooser.sh". Get it from: /usr/portage/x11-base/xfree/files/4.2.0-r6/chooser.sh and copy it to /etc/X11/