Posted: 17/07/2016 at 14:55
Depends what they are and where you are (eg Basil rarely does well in the ground in the UK and toms are hit-and-miss depending on the weather) but in general, in the ground is best. That way the roots can spread as they like, there is much less chance of them becoming short of water and nutrients as well as the secondary benefits of symbiotic soil bacteria and fungi. Of course, there can be negative effects such as soil-borne pests and diseases.
Of those you mention I would say the beans are better in soil, tomatoes better in pots and cucumbers are 50/50 but need large pots if grown that way. Brassicas always better in soil.
In my experience the best way of preparing soil is to dig-in well-rotted manure in the autumn and then lay a mulch of the same over the top before winter. The soil will then be easy to lightly cultivate in spring when you can sow seeds or plant out veg started off in modules and/or pots.