Quick fixes
Q What’s the easiest veg to grow in terms of speed of results, hardiness and crop yield? A in terms of hardiness, leeks, turnips and kale are good choices. if speedy results are important to you, try growing salad vegetables, and, for a prolific crop yield, opt for courgettes, root veg and potatoes.
trying to fulfil all three of your requirements defeats the object in a way, as vegetable gardening is about having a large and diverse range of crops which each have their own habits and characteristics.
Why not try all of the above, which should mean you get plenty of produce.