Dark Knight vs. Paladin
If your here it means you actually care beyond looks what the differences between Dark Knight (DK) and Paladin (Pally) are.
First off this guide is based off having used both Transformations and and seeing how each works to a large extent.
Ok, here we go: Both DK and Pally have a first level skill that causes Aoe damage to almost everything in a room. This is activated by using any Smash Attack. Both also gain unlimited Stamina.
Pally's do slightly more damage (very slightly) and thats all that it does, is damage. DK's do damage as well, however part of that damage is added to your Attack and Magic Attack, meaning the more smash attacks you use the more damage you cause, this applies to your Aoe skill as well.
Once you reach level 5 of your transformation you can start putting points in something besides Steal or Grasp (respective to which Transformation you choose).
Here is where one large difference is, Pally gets a skill to increase their Deffence while DK gets one to increase Attack and Magic Attack. Overall the DK skill becomes negligable because both Transformations get a skill that increases your base stats by much more. However Pally still benefits from the Defence boost.
Which brings to the last difference, Slow and Petrification. Both do similar things, Petrification stops an enemy, Slow Makes them Move and attack at a crawl. These two skills really aren't a real issue, as they dont work on bosses anyway, so are only useful on one boss. As it's only one boss this shouldn't matter.
So the Break Down, (and a special note for Fiona and Evie):
When you choose be honest with yourself, are you good at dodging? (For Fiona replace "dodging" with "blocking") If you said yes choose Dark Knight as you will get more out of them.
You could say the choice comes down to skill (please be honest when you choose), with DK for more skill and Pally for less.
Dark Knight slowly gets stronger the longer it is used, the same cannot be said of Paladins.
For Fiona Heavy Stander causes Steal and Grasp to activate, meaning you could (if so desired) just sit and let a boss hurt itself for 2 minutes. If you think thats a good idea, don't. Its just a nice added benefit for Fiona.
For Evie the Potential and Revelation skills make you Mana Shield exteremely strong, as well as regenerate very quickly (both Transformations get this so it doesn't matter, just nice to let you know).