I have found that when I look at a RPG, I look at the number of books it takes to run it. Its a cost thing although I also think about how much material I will have to learn and remember to run a game. Why? Because I'm a cheap and lazy DM. I don't want to spend a lot of time or money to prep for a game session. Is that wrong? Its just that we do this stuff for fun and I don't think it should become like a second job.
I might have a chance to run a game for my local RPG group. And I'm thinking of running Swords & Wizardry. Its free to download (good), there isn't alot of pages (less ink and paper). I am also looking at Mazes and Minotaurs. Its also free but has a much higher page count with lots of supplementary material. And the rules are in colour. So its mor of a back burner project.
There can be may things to consider when picking a RPG to run. Economics (money and time) was not one I used to think of. I guess I'm getting old.