Although the spectrum of greens available in the summer is impressively large, choosing the best kale or lettuce is a pretty similar process. The leaves and stems should always be crisp and hold their shape easily; avoid items with wilted or slimy leaves that droop all over the place. This is especially true of the heartier, denser varieties like Swiss chard or kale. If the greens are sold as heads (like lettuce or bok choy often are), give the bottom a quick peek. This is the part that was cut off the plant and it can be a good indicator of overall health: look for crisp and fresh rather than brown or mushy.