You should not use Spymemcached with Couchbase. You can, but I would recommend against it. First off, CouchbaseClient uses the Spymemcached jar because both Memcached and Couchbase use the memcached binary protocol for key-value operations. When we initially started writing a Java Client for Couchbase it didn't make sense to re-implement something that was already written so we used Spymemcached because it performs very well. You can think of Spymemcached as doing all of the basic stuff like sending messages and Couchbase Client as adding all of the nice functionality that makes it really easy to use Couchbase.
What if I use default Spymemcache client to cache ?
Everything goes through the cache regardless of what client you use so there is not point in using two different clients.
What could be pros and cons over the using couchbase client?
If you don't use CouchbaseClient you will be using something a lot more primitive. Think about it this way. Couchbase has spent about 3 years adding features to CouchbaseClient that make it really easy to use the Couchbase. CouchbaseClient will deal with topology changes and also adds operations that Spymemcached does not have.
Can the Spymemcache client handle server nodes and node failures itself?
No, but if you send traffic through Moxi then you will be able to deal with node failures.
I wouldn't even both with Spymemcached if your using Couchbase.
