the 301 is straight stitch and does a beautiful stitch. I quilt so that's really the only stitch I use except every now and then.
there was a really good article/comparison for 401 and 500 but can't remember where I saw it :-( they take the same cams and the 403 and 503 have fewer built in stitches compared to the 401 and 500) but they're available on cams. the rockateer has the neat shape to it. if you're not wanting to collect I'd just hold out for the one that appeals to you the most. 301s seem to be a bit higher priced along with the featherweights...for myself I'd grab 'em all (already have them all thanks to my mom and dad's eagle eyes at sales...) just need more time to sew on them