I actually started in Riak before Mongo, and what made the decision for me was...not having to install Erlang. I realize that's not really a compelling argument, but when I was evaluating alternate DBs, the one that gets up and running the fastest is likely to get a little more attention from me. Once I got spun up on Mongo, I didn't find a compelling reason to switch away from it.
"Download and unpack the package, run the binary, and you can instantly start playing with the examples from the console" is a hell of a good way to get people interested in your software.
Ease of first time developer installation should never be the deciding factor in these decisions. I realize it is pretty rampant, but it's not something we should be proud of.
Yeah but how long should I spend on software that I know nothing about the quality of if it's not easy to get up and running? Do you spend a day? two days?
While it's mostly just from experience I find that virtually no one makes a decision based on how easy it is to get up and running with a piece of software but it is an impression that stick's in people's minds and gets repeated when they talk about it later.
I completely agree, and I'm not saying that MongoDB is better because it has an easier install. The question was just "Why did you go to MongoDB over Riak?", and I did because I was able to start evaluating it faster, and discovered that it met my needs handily, deprecating the need to wrestle with my Erlang install any further.
"Download and unpack the package, run the binary, and you can instantly start playing with the examples from the console" is a hell of a good way to get people interested in your software.