I find that I don‘t do well with the too light systems. I need a bit more structure and so do most of the people I have played with in the past. However, among the heavy systems there are certainly still those with lots and lots of rules and those whose basic ruleset can be grasped by reading through a few chapters once. Just my 2c on the topic of rules. But then I also enjoy then not using those rules and just freeforming most of the time.
I am also a fan of RPGs that bring their own setting to which the system is adapted. If you have an idea of a setting you would like to use that may just decide for you.
What kind of story do you want to tell? What do you want your players doing? Puzzle solving? Involved combat? Magic? Lots of group interaction? Exploration?