one of my "must haves" is knee lift for the presser foot. Unfortunately it seems to be only offered on higher end machines. I also like good control with the foot pedal, from slow to fast speeds. I did a lot of testing with my straight stitch machine as I expected certain results and would not settle for less.
But I'll also say that I'm really having fun with all the bells and whistles on my embroidery machine, which I didn't test for sewing at all. I'm only using it to enhance quilt making, and so far it's sure fun!
One of the perks of getting older and more affluent (kids gone, still working) is I can afford some of those toys that were not in the budget when I was raising a family. If everything went south and I could no longer afford any of them, I'd be back to sewing on a Singer 15 and while I might not have as much fun, it would do the job.