Execution. I'm a total language nut. So learning each was fun on it's own. Go's package management was a heart breaker for me (at the time). Coming back and fixing an issue in Go was ok until my build machine on EC2 messed up for one reason or another. I had to redo it and took so long to get everything compiling again.

I looked at Rust for mainly Cargo, but ended up staying for the C interop. I was able to take PDF libraries (namely libharu and mupdf) and just link to them (after using bindgen). This gave me a really good binary that was reproducible from scratch easily.