Border? Again?

Sorry for this question but if I want to create a border in my world, what block i should use?
-Structure Void block?
-Border block? (From McEE, in Minecraft Bedrock 1.15 Beta)
-Barrier?

 

Structure void:
https://minecraft.gamepedia.com/Structure_Block#Structure_void
Barrier: https://minecraft.gamepedia.com/Barrier
Border: https://minecraft.gamepedia.com/Border

 

You can use invisible bedrock for this case. Other blocks you mentioned won't work as they are not implemented.
Or you can use WorldProtect plugin and set up the borders.

WorldProtect:
https://poggit.pmmp.io/p/WorldProtect/2.3.8
Invis. Bedrock:
https://minecraft.gamepedia.com/Invisible_Bedrock

 

I can add that, i'm not a newbie, also i want to make a border for uhc so it can't invincible :3

 

Depends on your case