[jseims]

What I would find more important than a comparison of technical features is a comparison of their active communities.

How many people are using each project, how active is development, that sort of thing.

[wheaties]

At good metric for an indirect peg on number of people using something is the "star" count on Github. It's not an ideal metric but it is a reasonable proxy. The other thing I'd look at which requires more effort is to look at the number of subscribers to the mailing list (if you can get it.)