So, I've completed all of the available content with the following party:
Here are some thoughts on these characters.
Good character, the only one who has strong Disable, which is pretty important. Also has good Acrobatics and Stealth, which don't come up as often, but can be useful. High Dex makes her very strong in combat, although she sometimes has trouble finding one of her weapons. Fortunately with her Sneak Attack and a decent Strength score, she can often defeat an enemy without even using a weapon, and of course in a pinch she can Evade. I try not to do this too often though, because it's important to get through the decks as fast as you can. Biggest weakness is probably that she has a lot of Items, which aren't all that useful until you start getting some good stuff later on.
Good character. Best Divine caster in the group, and with a decent Strength score she can hold her own in combat. Her healing ability is ok, but again you need to get through decks as fast as possible, so you can't afford to skip too many explores. Her bonus against Undead is very useful, and her high Wisdom makes her very good at closing a lot of different location types. Weakness is her low Strength score, which limits the benefit of Blessings in combat.
Great character, with a very strong kit overall. Good strength and melee, and the ability to add a d6 to any check is amazing. More than makes up for her lower strength, as compared to Valeros or Amiri. Not a great spellcaster, but can Cure herself to get back all the cards she's discarding with her Inspired Grace. Crusade is situationally useful, good for burning through a deck looking for a villain/henchman. Good Charisma is important for acquiring Allies and closing locations with Diplomacy. Weakness is, as in the pen and paper game, a reliance on multiple ability scores. Strength and Wisdom are both important to her, and both are only d8, but as noted above, her Inspired Grace can make up the difference.
One-trick pony, but is very very good at that one trick. She kills stuff, regardless of what cards you have in your hand. Not a lot of finesse here, just blasting stuff over and over until everything is dead. High Charisma is useful for some things, and her Arcane triggers off Charisma as well, so she has two useful skills. Weakness is that she is pretty bad at everything else. With only three spell slots, you can't afford to carry a lot of utility spells, and her other ability scores are all pretty low. She also burns through cards pretty quickly, and doesn't have a good way to get them back.
Wonderful support character. Reliable in combat, since he pretty much always has weapons available. Base Dex is only d8 though, so while he's generally good, he has the same issue as Kyra in that his base combat die is low. He's much better as a support character, with two excellent powers. Sniper's Shot is excellent, especially since it only requires a Recharge and not a Discard. Scout Ahead is also great, allowing you to see what's coming so you can plan accordingly. Weakness is that his skills aren't very good. He has Survival and Perception, but with a d6 Wisdom they're just not reliable.
Versatile caster, has so many spells that he has a lot of room for utility. There aren't a ton of great ones early, but later on things like Fiery Weapon are excellent. Can hold his own in combat because he usually has a lot of spells available. His Powers are all very good, Expanded Spellbook can extend his turn if he has stuff like Detect Magic available. Eldritch Exuberance is amazing in certain locations, but he really needs this stuff because he doesn't have any Blessings to gain more explores. He does have Allies for this though.