Randall's pistol shrimps naturally (in the wild) pair with Yasha Hashe gobies and yellow rose (high fin red banded) goby.
Tiger pistol shrimps pair with Yellow Watchman gobies (and I'm not sure what else) in the wild.
These are the more natural pairings. I'm not saying other shrimp won't pair with other fish...but for better success it's good to stick with these pairings.
As an example...I had a Randall's pistol shrimp with a yellow watchman goby for years, but my goby wouldn't stick with my shrimp all the time. I'd find him in different parts of the tank, completely away from my shrimp, sometimes for days on end.
It's also good to keep Randall's shrimp with gobies that stay small. Some of those watchman gobies can get HUGE (thinking of Graham's monster watchman) and can actually eat the shrimp.
Anyways...that's your goby/shrimp lesson for the day.