The best food tour that I took in Paris was the Evening cooking class and market tour offered by Cook'n with Class. You go shopping with the chef who gives you an education along the way. You then go back to the cooking school andprepare dinner in a small group. Great food and wine and even though it is expensive, they are extremely generous with the food and wine and it is a lot of fun. It is a small group (around 8).
I took a market tour and demo with Le Cordon Bleu. You tour a local market with a chef and translator. After the tour, there was a demo. I enjoyed the market tour, but didn't really care for the demo. The chef just prepared one plate of each course. There were about 30 people in the class, so no tastes and no written recipes were provided.
I took the Saint Germain tour offered by Paris by Mouth and was disappointed with it. it was ok. I thought they were somewhat stingy with the tastings considering the price and I just did not learn as much as I did with the Cook'n with Class tour. However, when I took this tour, I'd already been to Paris a number of times and had been to a number of the shops on the tour (Pierre Herme, Androuette, Patrick Roger) so to be fair, this might have been more interesting for a first time visitor.
I took the Chocolate tour offered by Paris Walks. The tour was excellent and it is a great value.
If you want to learn about food shops in Paris, I highly recommend David Lebovitz's website.
http://www.davidlebovitz.com