Tough choice, we very much enjoyed both.
Teppan Edo is quite good and a bit more authentic than your average strip mall Japanese steakhouse but not all that spectacular if you're used to that style of dining. It remains one of our favorites precisely because hibachi restaurants are a vacations-only experience, as there are none near by. The food is simple but well prepared, the service is ridiculously attentive, and my kids absolutely love the show.
Chefs is the stronger of the two on food alone in my opinion. I'm not especially fond of French food but was very pleasantly surprised by our meal there. The French onion soup is incredible and the croque monseiur (sp?) was very nice. And the desserts were excellent; we had the apple crepe and the profiteroles and both were delicious. The service was a little on the slow side, but seeing Remy was kind of cool.
For overall experience I'd go with Teppan Edo unless you have a good hibachi restaurant at home, in which case the experience wouldn't be as novel and the food/pricing might disappoint (no soup & salad included like at "real world" hibachi, no (unauthentic) fried rice, and of course the Disney property price premium). But I don't think you can go wrong either way.