basilmarket

Ecarina

So to summarize:
[b]Kanna[/b] and [b]DA[/b] links are the best (+10% dmg at lvl 2 each, and yes they stack)
[b]Xenon[/b] is probably the second best depending on your class (doesn't benefit DAs in the slightest, some classes benefit more from % crit, etc.) (10% allstat at lvl 2)
[b]Phantom[/b] is % crit, which is very useful for high crit dmg classes like i/L and Jett, but it's debatable whether it's better than DS or Lumi (15% crit at lvl 2)
[b]Demon Slayer[/b] is great, provided you like to boss. It's only this low because it doesn't help during normal grinding (15% boss dmg at lvl 2)
[b]Luminous[/b] has pretty much the same issue as DS, helps a lot against bosses but not much against regular monsters (15% pdr at lvl 2)
[b]Zero[/b] link skill is pretty great, and the character card (+8% exp at S) is useful (-15% dmg taken and +10% pdr at lvl 5)
[b]Cygnus Knights[/b] have quite a useful link skill, but in order to make full use of it you have to make all 5 cks and you can't give the link to other cks (+25% ele/status resist at lvl 10)
[b]Mercedes[/b] is good if you're still leveling up and if you don't have a tele rock, but if you're just planning on bossing and have no trouble getting around, you probably don't need it (+15% hp and a tele to Elluel with a long cooldown at lvl 2)
[b]Beast Tamers[/b] are mostly just this low because you can't make them right now, but their link and card are very useful too (+6% pdr at S for card) (+7% crit +7% boss +4% hp/mp at lvl 2 for link)
[b]Shades[/b] have a link skill that is mostly useful at bosses where you can die a lot, but it is very situational (15% chance to fully heal instead of dying when killed)
[b]Resistance[/b] classes don't have a link skill in KMS yet but theirs is mostly the same as Shades, once it comes out here of course, mostly useful at bosses (6 seconds of invincibility when reviving from death)
[b]Cannon Master[/b] is a pretty good link skill, it's mostly this high due to my own bias, but still. (+25 allstats +10% hp/mp at lvl 2)
[b]Jett[/b] can be very good but most of the time their link is kind of useless (+3 atk/matk +3 allstats base, can be changed for up to +20 of any of those, but you can only lock it for a week without nx and it resets every day if you don't lock it, you use those Star Dust things that drop from monsters)
[b]Hayato[/b] link can be useful, and it's a bit less of a pain to get since they don't have a lvl 2 link yet, it's not great though (+5 atk/matk +10 allstats at lvl 1)
[b]Kaiser[/b] link can be good for low-hp classes and is the best after Kanna for DAs, but it's not the best link out there (+15% hp at lvl 2)
[b]Angelic Buster[/b] link is pretty bad, it's fun to see your damage spike but it takes a ridiculously long time to cast, there was a glitch where you could get the buff infinitely but that's gone now, it's mostly just useful if you use it during the time when a boss is summoning, otherwise the damage boost doesn't really make up for the casting time (+45% dmg for 10 secs at lvl 2)
[b]Mihile[/b] link can be good, it's mostly this low because I main warriors and a cannoneer and I don't want to make a male character so I don't have one. If I remember correctly, it's (100% stance for 110 seconds, 180 second cooldown at lvl 2) but it could be different. It's mostly useful for low stance classes like mages and thieves.

This is mostly opinion past the top 6, all link skills are useful, tell me if I forgot anything.