Going purely on the table on the linked github page, without further reading into anything at all, Base32768 seems like the clear winner for a go to scheme.
Only if your browser game requires UTF-16 strings.
More specifically: only if you will be storing/transmitting data in UTF-16. If you're using UTF-8, base85 is much better.
Javascript strings are UTF-16 (or maybe it was UCS-2?)
Javascript strings behave like UCS-2, but they can be stored in memory however the interpreter likes, and they're typically written to disk or the network as UTF-8.