There are many factors to consider.
I will give you a few considerations:
- It depends what are the vegetables (You need to cook a potato )
- where are the vegetables produced (IMHO If you buy from China, I would extra cook them, sorry if I offend people here )
- how are they maintained ( If they are not fresh, you should cook them well)
- Organic vs non-organic (If you pay a lot of money for organic perhaps you want to extract the most enzyme out of these vegetable, don't over cook them)
Now about the cooking, it always depends what you have and what you want. If you have beautiful fresh organic broccoli, I would just slightly steam it and eat it. If you have a broccoli that has been sitting in your fridge for 1week +, perhaps a nice boiled soup would be better ?
You have to experiment with each vegetable. Google them up )
Good Luck