Back to varnishing

Along with being almost ready for drywall, we’re about ready to hang the pocket doors. That means it’s almost time to get out the sandpaper, tack cloth and varnish. I am so happy with how the spar varnish turned out for the exterior doors, that I’m not sure what to use for the interior. We used varathane for the staircase, abut we still have to do the mantel and three interior doors. I know there’s a lot of you that have more experience with this. What have you used for interior door finish and are you happy with it? We are not staining the doors, they are fir and we want to keep the natural look/finish. Thanks!