I used pfSense in a very different context (vpn gateway) and I used the vmware image option. I haven't used the multiwan feature and I don't know if it can be installed on (almost) any router as openwrt.
I did tried dd-wrt for this same purpose, the interface is much better, it is very flexible as openwrt, but I couldn't put my wifi on client and AP mode at the same time and I needed to connect to one of my WAN using wifi because that modem is not close enough yet.
that's quite disingenuous. it uses pf, openSSH, and LibreSSL (in development version) from OpenBSD on top of a FreeBSD core, and it's wireless card support is not very much below linux (though you might need to work to get it up).
if you have older x86 hardware, it's hard to top pfsense.
I did tried dd-wrt for this same purpose, the interface is much better, it is very flexible as openwrt, but I couldn't put my wifi on client and AP mode at the same time and I needed to connect to one of my WAN using wifi because that modem is not close enough yet.