I have and use a Pfaff 138-6/21. It is a straight stitch and zigzag industrial and does not use an oil pan. It uses proprietary feet which are as scarce as hens teeth. I only have the multipurpose foot right now, but I found a straight stitch foot on Ebay that will soon be mine. It is the quietest machine I have. When it is running - even with the 1/3 horse power clutch motor - all I hear is a little tick, tick, tick. I can't hear the motor running if I am in another room. I left it on one evening when I went to the kitchen to fix dinner. 2 hours later I came back in the room to find it still running and shut it off.
I also have and use a Singer 31-15. It is straight stitch only, and it doesn't use an oil pan. It uses regular high shank industrial feet so the possibilities are endless for feet, it is not as quiet as the Pfaff when the motor is engaged, but it runs a tad faster at full out speed. I have it set up for FMQ. I removed the feed dogs and bought a needle plate with only a hole in it for the needle. I don't get to practice my FMQ much since the Singer and the Pfaff are the same size. Because of that, they share the same industrial table and the Pfaff tends to be in the table more because of the type sewing I do - other than quilting.
I would love to get my hands on a Juki with a walking foot. One of these days.