IRELLA KUR
Shields: 90
Armor: 18
Health: 195
Damage: +10%
Parent: Wynn Syphex (Valkyrie)
Learns Slam at level 4, learns Crowd Control at level 6, learns Rule of Law at level 8
The Juggernaut's toolbox is nice, but it's still pretty situational sometimes. Irella makes for an option if you'd rather the Juggernaut was able to do double-duty as big damage. Faster access to your big-hitting moves, plus Rule of Law for some major spike damage, is all very nice. But giving up Unleash is a bigger cost than you'd expect at first, and you'll really miss it when it's gone. You also have CONSIDERABLY lower shields, so this isn't ideal if you're relying on shield regen helpers to patch you up.
SEPHI KUR
Shields: 110
Armor: 9
Health: 170
Damage: +20%
Crit Damage: +20%
Parent: Tark Chanlo (Marksman)
Learns Rule of Law at level 4, learns Pound for Pound at level 6
What's that? Irella still doesn't feel damaging enough? Okay, wiseguy, here's Sephi. Even better damage, but in exchange, you lose Unleash AND Crowd Control. That's right, no AOE, no buff cancellation, and the moves you get to replace them are SLOW. And you lose half your armor. Sephi is great if you want your Juggernaut to hit like someone who's wearing a cannonball as a suit of armor, but is the worst at the conventional tanking/support you learned Juggernaut with.
TISHA KUR
Shields: 100
Armor: 13
Health: 160
Damage: +15%
Crit Damage: +15%
Parent: Sidara Kymon (Gunslinger)
Learns Pound for Pound at level 4, learns Unleash at level 6
Yeah, all the Juggernaut progeny have damage boosts. Got a problem with that? Tisha at least still keeps the more valuable tools of the class, without sacrificing nearly as much shields or armor as her alternates. So on a sliding scale of tank to damage dealer, the order is Aia, Tisha, Irella, and Sephi. That's it, that's your metric. Sure, there's fine details of when you learn each move, but broadly, that's where you need to have your head at when choosing alternates.
H'PPA KUR
Shields: 95
Armor: 18
Health: 190
Parent: Rav'n Tysanno (Guardian)
Learns Crowd Control at level 4, learns Unleash at level 6, learns Slam at level 8
Obtains elements on odd levels, as per the Guardian's ability
Oh, and then H'ppa is just completely and wildly different. Not in terms of tanking, no, on that front she's about the same as Aia, slightly lower max shields in exchange for more health, slightly shuffled movelist, et cetera. Hardly worth breaking down. The fact that you can get your pick of an ever-increasing range of elements, on top of what your gauntlet slot already provides for you? That there is unheard of. I'll discuss the ability when we, y'know, actually GET to the class that has it, but long story short, it's good and you want it.