My choice would be the 15-91. It may be a simple machine but so is the 201. However, I quilt and mend hubby's work jeans. The 15 will power through his jeans just awesomely and I can't beat it for piecing or quilting. Love it's straight stitch ~ so precise and fine.
I do agree with Iswan, post #14, about the 301. If I had the table or a cabinet for it, I'd use the 301 exclusively but not having either, I use my 15 the most.
Chris