What I want is not a comparison between Redis and MongoDB. I know they are different; the performance and the API is totally different.
Redis is very fast, but the API is very 'atomic'. MongoDB will eat more resources, but the API is very very easy to use, and I am very happy with it.
They're both awesome, and I want to use Redis in deployment as much as I can, but it is hard to code. I want to use MongoDB in development as much as I can, but it needs an expensive machine.
So what do you think about the use of both of them? When to pick Redis? When to pick MongoDB?