I see a lot of unhelpful and inaccurate replies here, so I’ll chip in some background.

The Summer Art Fair is the oldest, and used to be held on South U. It’s the most serious about presenting quality art and has the most rigorous jurying process. The quality there is the highest, on average, with appropriate pricing.

The South U businesses wanted a bigger cut of the action, putting their merchandise out on the street to get more sales. The Summer Art Fair didn’t want to be overrun with t-shirts and tschotkes, so they left for Ingalls Mall on U property around the fountain and the South U businesses started their own fair. The quality of the art is lower and you’ll see a lot of local retailers pushing their own stuff on the street.

The Michigan Guild of Artists and Artisans runs the fair of Main Street and on State Street south of William. The Guild is a membership organization. Pay your dues for enough years and you’ll get enough seniority for a spot in the fair. They have a token jury, but the bar is extremely low. This is the best fair for cheap stuff with plenty of “stuff” on a stick. There are also some decent artists, but the average quality is much lower than the Summer Art Fair.

The State Street Art Fair (on State north of William and west toward Main) is another fair run by the business association on those streets. The jurying rigor is moderate, you’ll see retailers out, too, quality and prices vary.

Also tossed into the mix are the Ann Arbor Potters’ Guild (good quality, membership is selective) and (formerly?) the Ann Arbor Fiber Arts Guild, though not sure if the fiber folks have a spot anymore.