Yeah, FairVote is.... Okay. In terms of objective vs political, they tend to be as political as they can get while still being objective. They used to actually say a few things that weren't exactly true, but opponents kept calling them out on it so they quit as far as I know. Wikipedia would be a better source, though be aware that proponents of any system will try to sneak in promotional language. But, at least on Wikipedia there's also people trying to keep things objective.
These are what I would consider the most relevant articles if you're looking to understand the realistic options in America.
I would say that you don't actually need to read any of these articles particularly closely. They can get very technical. You can just skim them for the parts you find interesting.