Question

Are the Beast Balls worth acquiring for catching the Ultra Beasts or can Ultra Balls be used?

Comments

If my memory is correct, the Beast Balls are just given to you, so I'd say that they're worth using.

Answer 1

Against Ultra Beasts, beast balls are 5 times as effective as ultra balls, so they're definitely the second best Poke ball for catching Ultra Beasts (second to master balls, of course).
source

Answer 2

YES. I mean, they are given to you for free, so you have that.
It's near impossible to catch an Ultra Beast without an Ultra Ball (And Vice Versa)
But if you want to be an absolute showoff, you can catch them in premier balls. (It IS possible, just a VERY VERY Low catch rate)

Edit: I know this is necro, but It's near impossible to catch an Ultra Beast without an Ultra Ball was meant to be It's near impossible to catch an Ultra Beast without a Beast Ball