I would say OpenWRT wins in this category. It's not based on open sourced Linksys firmware anymore, it's a embedded distribution designed from scratch for modularity and portability. It really is a awesome piece of engineering which is fun to use and well documented in detail. If you want to extend the features of the router and add things like openvpn, ntp server, traffic shaping, asterisk pbx, tftp server or whatever comes to mind, openwrt most probably has it packaged and ready to use.