use Redis when you need advanced data structures built in. Memcached is just a KV store.

Memcached is a LRU cache.

I went and searched for memcached redis because up until now I haven't gotten around to checking out the differences. Here are some things I found.

http://antirez.com/news/94

http://stackoverflow.com/questions/10558465/memcached-vs-red...

http://www.infoworld.com/article/3063161/application-develop...