If you could have any spawner which one would be most worth it? Including any mob with a spawn egg.

My friends and I are on a multiplayer server and we've allowed players to buy spawners with diamonds. (60 diamonds for a skeleton spawner, 100 for an enderman etc). Which do you guys think is most worth it? We're playing on bedrock on a realm. IDK what the prices would be for some out of the box ideas, but I doubt it would be more than 2 stacks of diamonds. I already have an iron golem farm in my village btw too.