whens it time to ditch redis for memcached

i've been using Redis for a while now, and it's been fantastic for things like session storage and leaderboards. but lately, i've been wondering if i'm over-engineering some of my caching needs. for simple key-value lookups where persistence and complex data structures aren't crucial, is Memcached a better choice. when have you found Memcached to be a more appropriate fit than Redis, or vice-versa