The 15-91 only does a straight stitch but can pretty much sew through anything you can fit under the presser foot (which is quite a bit) and it does have true reverse. In pristine condition they can be pretty pricey but even if you find one that needs a bit of work, snag it. Parts are easy to get and these machines are really easy to service. I bought one for 15 bucks at a thrift store, put about $40 worth of parts into it and it runs like new. There's a lot of good info and a review here:

http://blog.sew-classic.com/2008/10/...ne-review.aspx

Keep up the good work!