We prefer 1900. The characters are great. The food is really good at 1900. I haven't been to Chef Mickey in a few years, so I won't comment on how their food is today, but it wasn't very good the last time I was there. The atmosphere is good in both. It's all preference.
1900, hands down, especially for adults. We never returned to Chef Mickeys after our first try, so it could be much better now, but our experience at 1900 Park Fare was a million times better from the food to the character interaction. The only reason I would go to CM is if you have members of your party who really want to see Mickey and friends and you don't want to use park time for that.