Linux users can’t even agree [...] so how am I supposed to pick one with any confidence?
Easy. You make a post like the OP, count the positive mentions of distros in the comments, and bam, you have your distro of choice. It's called the Linux newbie roulette and works kind of like the magic hat in Harry Potter that sorts you into your house.
I think the problem might be your PostUp/PostDown lines have an in-interface (-i) but are missing an out-interface (-o) for the forwarding. Try this: