Rizen
Smash Legend
wallOtext
Zair and Fair both have their individual uses. A rule of thumb is Zair hits farther sideways and is better covering horizontal spacing and characters with good reach (Snake, Peach, Ike, etc) but Fair still has good disjoint forward, larger attack area vertically and cuts twice so it walls out smaller characters (Wario, Squirtle, etc). Or for spacing (far to close sideways): arrows>boomerang>(Bombs cover everything here in), Zair>Ftilt/Fsmash>Fair/Bair/jabs/Dsmash>Utilt/UpB/Nair.
Zair is great on shields but it only attacks on the extending claw hitbubble so annoying hoppers like Wario can avoid it more easily then larger less mobile characters. Fair cuts 2 times in the same basic area in front of Link and has more delay making it a better hitbubble 'wall'. Fair can be a good forward KO move but doesn't chain into other attacks like Zair. Both landing cancel if they miss or for faster followups and both should be spaced to hit with the outer part of their reach.
tl;dr, farther Zair, closer Fair.
That's like asking "Who does the better version of the song 16 Tons, Eric Burdon or Leon Russell?"Should I use zair or fair on an opponent in front of me
Zair and Fair both have their individual uses. A rule of thumb is Zair hits farther sideways and is better covering horizontal spacing and characters with good reach (Snake, Peach, Ike, etc) but Fair still has good disjoint forward, larger attack area vertically and cuts twice so it walls out smaller characters (Wario, Squirtle, etc). Or for spacing (far to close sideways): arrows>boomerang>(Bombs cover everything here in), Zair>Ftilt/Fsmash>Fair/Bair/jabs/Dsmash>Utilt/UpB/Nair.
Zair is great on shields but it only attacks on the extending claw hitbubble so annoying hoppers like Wario can avoid it more easily then larger less mobile characters. Fair cuts 2 times in the same basic area in front of Link and has more delay making it a better hitbubble 'wall'. Fair can be a good forward KO move but doesn't chain into other attacks like Zair. Both landing cancel if they miss or for faster followups and both should be spaced to hit with the outer part of their reach.
tl;dr, farther Zair, closer Fair.