In AD4 there are excellent cards in every category. I simply can't decide on any one card. If you can pick one, like and respond.
Ranged - Shortspear +3. The only choice, but it's a good one.
Melee - It's hard to go wrong with any of them. But I save Greatclub +3 to the end, and keep Demonbane Longsword +2 in my deck because it is rechargeable. At the end, you get a very nice MokMurian's Club.
Divine - Restoration. But you have to remember to use it before the encounter.
Arcane - Poison Blast. Unfortunately, a variety of monsters resist poison.
Light - Robe of Enery Resistance. AD4 doesn't offer a lot in this category before the end reward Robe of Runes
Heavy - Ebon Thorn. Very nice +2 to melee attacks
Shields - Reflecting shield. I favor this type of shield over any other armor. But you get a better one in AD5
Items - so many good ones here
Amulet of Inescapable Location, Flask of Fire (or Frost, or Magic), Greater Sage's Journal, Magic Spyglass, Necklace of Fireballs, Staff of Heaven and Earth. Ezren starts to shine with this collection to build with.
Eagle - among so many good allies, this card is a winner. Putting Eagle on Lini is a bonus!.
Blessing of Gozreh - I'll always keep at least one in my party.
Looking through this list, my post selection best card is Eagle. I've played a short deck with the Paladin and LIni. The Eagle is always a big factor when it enters play.
Thanks and I look forward to your comments.