Productive varieties for me include Blue Coco, Helda Romano, and Scarlet Runner.
If you like all vegetables equally, then certain varieties of beans, cherry tomatoes, and summer squash might give you the most return. It's a good idea to research specific varieties you are considering to see if they are known for high yields in your climate. These varieties were hugely productive for me in my cool-summer, long-season climate: Sungold, Sunsugar, Tommy Toe, Galina's Yellow, and Fox Cherry. I prefer pole beans rather than bush beans, because pole beans have to be planted only once, and they produce all season. Productive varieties for me include Blue Coco, Helda Romano, and Scarlet Runner. Bush beans might be a better choice for canning, because they tend to produce all at once, and you have to replant at regular intervals. Vining summer squashes are a good use of space if you can trellis them and use vertical space.