Great question, Clare! Well, let's see. I love my centennial Singer 201 for its beautiful stitches and the Singer 15-91 for the way it makes FMQ so much fun. Both are great straight stitch machines. In addition, I know I could not get by without my Bernina 830 Record which never gives me a moment's worry about tension and produces lovely stitches. It can do a few utility and decorative stitches too. And my ruby red Viking 6570 is equally reliable and worry free with a few more stitches. It's also portable which is a great advantage. But wait, that's four, isn't it? Honestly, that's as low as I would go -- and only then in case of dire necessity!
I'm eager to see what others say.