We loved the food at Tutto, but felt the atmosphere was more "serious" that most non-signature WDW restaurants. We had my then 1yo nephew with us and it was fine, but since we will have 3 under 3 on our upcoming trip, we have opted not to return to Tutto this time. Also, all of us thought that the prices were quite high here - even compared to other WDW restaurants. (We were on the DP so the cost didn't matter to us, and the food was VERY good.)
We really enjoyed the food, service, atmosphere, and entertainment at Biergarten. It was a tasty meal and a fun experience. It is buffet style and yes, if you are a smaller party, you will be seated with others. That can be hit or miss, I suppose. We will be going back this trip.
They are two different places in terms of both food and the overall experience, but IMHO, you can't go wrong with either. Go with the type of experience you are more interested in. (Have never been to Chefs, so can't comment on that one.)