From the three kinds of green i know, my preferred list is
- Mustard Greens - especially the type Mizuna - https://en.wikipedia.org/wiki/Mizuna, those can be used for soups and stews (just to have some green in there), omelettes (replacing the parsley) and as a side-dish like spinach
- Collard Greens - i like them most as a side-dish, replacing the pesky brocolli
- Turnip Greens - only the really young leaves, the older ones have a slightly bitter taste. And these too as a side-dish or as green into soups and stew.
The advantage of the turnip-greens is that you also get the turnips. I cook them for the ducks and i use them as replacement for potatoes in soups. The trick is to dice them, boil them shortly in salt water, let them sit for some minutes and the dispose the water. The remaining turnip dices have lost the typical turnip-taste and everybody (including my pickkky woife) has eaten them as potatoes.

Are there any other kinds of greens out there that i don't know about? (yet!)