I don't think you should just learn one; they are all used for different niches....

		A1kmm on March 16, 2011 \| parent \| context \| favorite \| on: MongoDB 1.8 (stable) released I don't think you should just learn one; they are all used for different niches. It depends how your app trades off different things (consistency, reliability of reads, reliability of writes, speed of reads, speed of writes, efficiency of hardware use, and so on). See http://news.ycombinator.com/item?id=2052852 for a comparison.

I'm not planning on just learning one, just trying to pick one to learn first