The Ballston market is preferable to many others around here because of the design. All booths are set up in a circle around a large mound of grass. It's so easy to maneuver, not cramped/crammed onto a tiny spot of land, and it's not overflowing with vendors selling crafty things and clothing. It's called a farmer's market for a reason, we want to see food! On beautiful days it's fun to see the business folk lounging in the center (my fave: the guys in suits taking off their socks and shoes to stand in the grass), and the live music's a nice touch.
Stand outs for me are Walnut Hill Farm, exquisite Fleurir gourmet chocolates, and Farmhouse Flowers -- but leave my Gerber daisies alone!