Greens are arguably the most important part of your salad. After all, its what makes salad . . . well . . . salad. Your greens are what tie everything together and serve as the centerpiece of sorts. Its nice to use a variety of complementary greens, like spinach and arugula, or romaine and green leaf.
You can experiment to figure out what you like best. There really is no wrong choice. Almost all salad greens are loaded with nutrients, and each has its own flavor and character that can shape your creation. Just make sure you buy organic, if possible, and wash them thoroughly before using.
You can also try using just one type of greens and then add other ingredients, like this cherry tomato, arugula, and sorghum salad.