I personally like peas and brocoli as far as greens go since I can get them frozen. Stuff like spinach does not really freeze well and if you manage to actually go through a whole container before it goes bad you'll have other set of problems, like kidney stones. Basically I just get what's in the frozen section, and mix it up. Sometimes peas, sometimes vegetable mixes with different stuff, sometimes broccoli etc. I will just use it as a side when cooking chicken strips or fish or whatever. Sometimes even unconventional things like eggs. Instead of bacon and eggs I'll make eggs and veggies lol. Sometimes just making a salad works too, but it's the same deal as spinach, most of the stuff you use to make salad with does not freeze well, so now you're stuck eating salad for like 2 weeks and it still goes bad. I guess that's where growing your own stuff would work better, I really want to get into that eventually. Then you just take what you need as you need it.
Juicing is an option too, but it's very expensive as you go through quite a lot for a single glass. It's easier to just incorporate the veggies in the diet that way you get the fibres too. But with juicing you get the nutrients in your body faster. Or so they say. There's lot of debate on that whole topic.