I have stayed at all four and it seems my favoprite is the last one I stayed in!! I can tell you that my least favorite is Port Orleans French Quarter as I found it to be bland. It was a good idea but not executed well IMHO. It is still a nice place to stay and the compact layout was convenient. I didn't care for the food court there. It was not bad but not great either.
The other three are about equal as far as design, atmosphere, food offerings and location.
Here are some pros and cons of the resorts.
The CBR has bigger rooms. The food court is good though a far walk from some of the rooms which doesn't bother me but is a major issue with other people. I saw a snake there.

The bus stops are close to all the villages. The main pool is fun though a bit small. There are lots of quiet pools but they seem busier than at the other moderates and they are a bit bland. There are 6 or 7 bus stops. It has expansive views across the lake.
CSR has only one sink in the vanity area. The quiet pools are very quiet. The main pool is fairly spectacular though crowded. The water slide is longer than the other moderates. The food court is good though a bit more expensive. the 3 themed areas are distinctive from eachother. It has expansive views across the lake.
POR has two distinctively themed areas both with loads of atmosphere. Staying in the Mansion Homes really does feel like you are staying at someone's estate. This has my favorite food court in terms of atmosphere. The food is fine too. The quiet pools are nice here. The boat to Downtown Disney is okay but over rated in my opinion.
POFQ is smaller and compact with newly remodeled rooms. The main pool is very fun and very crowded. There are no quiet pools though you can walk over to POR and use theirs (along with the full service restaurant).
In general they are all fine places to stay and you should pick the one with the theme that appeals to you the most.