I grow beetroot in preference to silverbeet, and use the leaves of those as well as the roots. In the right conditions tomatoes are also very prolific and produce a very worthwhile crop - as long as you are not spending a fortune on advanced seedlings and tomato cages I'm not sure how you could find them not worth it.
It depends a lot on your specific growing conditions and what you tend to eat - in the right conditions some plants grow like weeds and are very worthwhile, whereas in someone else's garden the same plant may be nearly impossible to grow. The most important thing is to work out what grows well for you, in your garden.