A comparison in the form of a bullet list:
Couple of remarks:
Both fully open source?
CouchDB is using the Apache License while MongoDB is using GNU AGPLv3. These have different implications
Which has better documentation?
Both have good documentation, enough to get started quickly. MongoDB seems to have more details on their documentation.
CouchDB already has two books available: CouchDB: The Definitive Guide: Time to Relax (Animal Guide) and Beginning CouchDB (with a Kindle version) .
3 5 books in the works:
Update: I’ve updated the list of book thanks to Damien Katz and Meghan Gill comments. It’d have been easier if I’d already had them around.
Note: the above links are affiliate links. Buying one of the books will get me a penny.
Which is faster?
This article tested around 250 MB size file. It is found MongoDB is faster than CouchDB. There is also another benchmark data test. It also found MogoDB is faster than CouchDB for the heavy load of query condition. This is another article impressed by the efficiency of MongoDB.
Unfortunately most of these benchmarks are incomplete or flawed. You should read our coverage on NoSQL benchmarks to better understand how difficult is to come up with good and unflawed benchmarks.
On the MongoDB official site, there is a fair comparison of the durability. CouchDB is with crash-only design. Database can terminate at any time, MongoDB takes a different approach. Reparidatabase() operation has to be run once there is an unexpected termination.
I felt like pointing out to our comments on MongoDB durability and also different solutions for insuring disk level durability