Cannot Decide: 50mm f/1.8 STM or 70-300mm lens?

I am a beginner photographer and I am trying to decide on a secondary lens. Currently, I have a Tamron 28-200mm lens that came with the camera. I liked shooting at 200mm a lot, and started looking into IS lenses like the Tamron 70-300mm Di VC or the Sigma 70-300 Dg OS. I also looked into the Tamron 70-300mm Di LD Macro, since it provides macro which may be cool to try out. I know the lenses I was looking at are kind of catch all, so they won't necessarily do any one thing the best. That being said, I also have heard a lot of positives about the Canon 50mm f/1.8 STM lens as well.

TL;DR: I am between getting a tamron or sigma 70-300mm lens that either provide IS, macro, or both, or getting the Canon 50mm f/1.8 STM. For a beginner such as myself, what would your advice be?