I've never sewn on a 401/403, but I LOVE my Rocketeer (500A). I confess I bought it purely based on the looks, but it's a great machine as well. It's the only machine in my herd that naturally has a perfect scant 1/4" seam allowance with my 1/4" foot - all the rest of them (new and vintage) need tweaking to get that. It runs smooth and the stitches are nice. I haven't used a lot of the decorative stuff but I DID use the blind hem stitch for the first time in my entire life on that machine and it went better than I anticipated.
I've become very fond of the slant needle, it's SO easy to see what's going on right at the needle. Plus it's easy to supply - takes standard size needle, class 66 bobbins, and the cams are everywhere.
I like a lot of my machines and deliberately make an effort to rotate through using all of them, but the Rocketeer gets the most use out of the vintage machines I have and I'm always happy to be sewing on it. (Even over my F-word machine, lol Miriam...)