Chez L'Ami Jean or Aux Lyonnais?
Both have great food, and both are very reliable. But they are equally different.
Aux Lyonaise, is very traditional, and is run by Alan Ducasse as a traditional Lyon bistro. The food is obviously very representative of Lyon. Service, ambiance and food quality is good (as you would expect from Ducasse). They typically turn the tables twice a night, so there is an early booking, and later tables at 9:30ish. Spacing between tables is OK for Paris - you are close to your neighbor but you don't have to choreograph your movements with the table next to you.
Chez l'Ami Jean, is different cuisine, mainly south west/basque influenced. The cooking is good, and probably a bit more modern/innovative. Service is fine, but fast - in contrast to Aux Lyonaise and they can sometimes turn the tables four times a night, with a 6:30, 8:00, 9:30 and even 10:30/11:00 tables (we were asked to move to the bar once - with free champagne as they needed our table back). Tables are squeezed together and you do need to carefully choreograph your moves with your neighbor (so close they could be communal tables). But it is fun and part of the charm of the place.
Both book-up so you need to reserve about a week in advance. Aux Lyonaise is more expensive, but by 20/30% rather than twice the price.
Go to both and compare. I used to frequent both quite often.
Haven't eaten at Aux Lyonnais but I do like Chez L'Ami Jean. Went with friends again in June and found the food grand, the company convivial, and the price fair. We visited with our neighbors (French on one side, Americans on the other), with folks recommending their favorite things (the rice pudding was universally approved) and the service was full of energy, attentive, and, on a busy night, zipping around us which only added to the sense of fun. Just a good vibe all around.