Rue Cler is much better in every way, but location matters for grocery shopping, so come here if you're nearby.
We had an apartment on St. Germain, about two blocks away, and did all our grocery shopping on Rue de Buci. The fruit (end of May, early June) is awesome and far better than even most farmer's markets I've been to in the U.S. The vegetables were more hit or miss, but always at least good. Roasted chickens sold from street display were perfectly adequate, but nothing special (less meat per pound than in the U.S., it seemed). At the fruit market, ask for help if you're not sure which fruit to buy to be eaten today (or tomorrow).
Paul's boulangerie on the corner was our daily source for breakfast, eaten in the apartment. The Carrefour grocery story has just about everything you can't find at specialty stores. Most of the pre-cooked dishes from the stores east of Paul's were unimpressive, which is too bad given the convenience. Roses bought at the flower shop here lasted almost a week.
Come here if it's convenient, but go to Rue Cler if you can.
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