I like this 5 player FFA map because of its symmetry:
https://resource.openra.net/maps/40310/
There is also a 7 player version:
https://resource.openra.net/maps/42781/
Updating Official OpenRA RA map pool
It's time to update the official map pool once again
Re: Updating Official OpenRA RA map pool
6 player naval FFA Shuriken https://resource.openra.net/maps/12789/