If you look in any guidebook for "authentic Paris bistro" you're likely to be sent to Benoit. It's been in Paris forever, was a favourite of politiians, bought by Alain Ducasse' prestigious company, and has even gotten a star from Michelin. But is it that good? Not really.
I've been twice in two separate years now and to be honest, the place suffers too much under the weight of its reputation. The clientele is 90% tourists, sapping the will and joy out of the staff there. The menu is classic bistro, which is to say a bit hackneyed. Everything is prepared well enough but nothing is particularly good. Nothing is bad either, and the service is very good. It's just uninspiring.
Paris is so full of honest and earnest places that there's no need to go to someone just making the motions. If you're looking for a good traditional meal in Paris and you're not sure how to find a place, by all means go to Benoit. It's certainly good. But if you want something interesting save the evening for somewhere new.