[Plugin: Memcached Object Cache] apc and memcache object cache

You cannot use both of these plugins at the same time. They both perform the same task, which is object caching. The difference is whether the object cache is stored in memcached or within APC.

You should select the one that makes the most sense for your setup. If it is a single server, APC is probably the best choice. For multiple servers memcached would be best, since it can be accessed from multiple machines, without duplicating data.

APC can be used without object caching, by default APC provides a method of storing the compiled PHP code in memory, reducing the execution time of PHP code. Regardless of object caching, I would recommend the use of APC.