At HR, why are there 2 armor sets of each? Whats the difference?

[Lycon]

They have exactly the same stats. The only difference I see is a little bit of color?

[Juno Brier]

It's a matter of whether you value that extra skill or the extra slot.

Like for example, for the Odogaron set, the Beta version of the torso piece may be more preferable because the Alpha version offers an extra point of Bleed Resistance, which is basically worthless because Odogaron is the only monster in the game that can inflict bleed anyway.
Meanwhile for the other pieces of the Odogaron set the Alpha version may be preferable due to offering extra points of Critical Eye and Speed Sharpening which are both quite useful.

[kampfer91]

Or you can mix both alpha and beta, as long as you have 5 pieces of that set you will trigger the set unique skill .

[Aunel]

Early stages of HR: Use Alpha. Or beta teo arms if you have dragonking eyepatch. Later on use Beta and build from your deco drops by farming the everloving ♥♥♥♥ out of t2-t3 tempereds. A hand built setup is superior to a pre built one, though alpha pieces are good spaced out here and there.