Here are tips for selecting the tastiest (and usually most nutritious) produce:
Buy root vegetables that still have their tops; the tops help preserve flavor and freshness.
Look for deep and unusually colored vegetables, such as purple carrots. Those are often varietals that are bred more for flavor than for yield.
Buy smaller vegetables with a higher skin-to-pulp ratio. (Think cherry tomato vs. heirloom tomato). These often have less water and a more concentrated flavor.
Make sure the cut ends of your greens are the same color as the rest of the stem. This area tends to become darker the longer the vegetable sits on the shelf.
Avoid limp, mushy, yellowing or moldy produce, but dont worry about asymmetry, a few bruises or other imperfections. A plant produces phytonutrients in response to stress, so a few bee stings or a bit of sunburn can be good things.
Smell your produce. It should smell the way you want it to taste. Better yet, ask for a taste.
Avoid produce sold in sealed plastic bags or clamshell packaging. You cant smell it; chances are its been sitting around for a while. Also, it might have absorbed some of the chemicals from its wrapper.
Try to buy food with a farm story. Who is the farmer? Where is the farm? What else grows there? At the farmers market, it is easy to discover this story, but even supermarkets are starting to use display signs to provide this kind of information.