Vitamin C is particularly fragile in both treatments; I flinch when I see people freezing orange juice because they've got it in bulk. My parents' generation used to boil vegies to within an inch of their lives, removing many vitamins in the process. Most modern cooking of green vegies (woks, steaming etc) usually leaves them with some crisp crunch by exposing them to only a minimum of heat. This leaves some of the vitamin content intact.

Most nutritionists emphasise the intake of fresh fruit and vegies as a major part of our intake and this is part of the reason.

Cheers, Rowan