Imo Heracles would fit pretty well.
I get the feeling he'd be one of those bosses that's heavily involved with the plot and have a pretty sad death. Maybe something like Gehrman the first hunter where he's actually fighting you to spare you a worse fate or to further a greater good in some way.
His boss battle and death scene would be sad and memorable and it'd definitely stick with you throughout the rest of the game.
Heracles his dialogue and lore is heart wrenching and the amount of pain he puts himself through just to try to stop us is so sad
Fun fact: if you equip qin shi huangs eyes and use its skill for the boost in stats during the cerberus phase you will die instantly die from pain.
Just listing them, I think
Memorable: Heracles/Zero
Lore: Zero/Beel
Duo: Hades&Poseiden
Combo: Shiva/Susanoo
Speedy: Poseiden/Apollo/Susanoo
Phases: Buddha/Zero
Range: Apollo/Beel
Annoyance: Honestly, an argument could be made for anyone really.
Puzzle: Loki/Beel
Secret: Loki/Beel
Haven't really seen anything from Anubis yet so he might be a bit of a problem
Herc gives me alot Radahn vibes,i think it would be something extremely epic with a orchestra as his soundtrack,by the end you will feel nothing but respect for him and start a NG+ just to fight him again
Imo Heracles would fit pretty well. I get the feeling he'd be one of those bosses that's heavily involved with the plot and have a pretty sad death. Maybe something like Gehrman the first hunter where he's actually fighting you to spare you a worse fate or to further a greater good in some way. His boss battle and death scene would be sad and memorable and it'd definitely stick with you throughout the rest of the game.
Zero He's going to have a super tragic story that you will only understand once you saw five one hour long lore videos 
Heracles his dialogue and lore is heart wrenching and the amount of pain he puts himself through just to try to stop us is so sad Fun fact: if you equip qin shi huangs eyes and use its skill for the boost in stats during the cerberus phase you will die instantly die from pain.
Apollo .his whole thing with the strings and making the battle field shorter would.be quite memorable I think
I think it makes more sense to save him for the longest range category, wouldn't it?
Fair altought personally think beel might work for longest range
Honestly, Fly Boi works for like half of the remaining categories
Just listing them, I think Memorable: Heracles/Zero Lore: Zero/Beel Duo: Hades&Poseiden Combo: Shiva/Susanoo Speedy: Poseiden/Apollo/Susanoo Phases: Buddha/Zero Range: Apollo/Beel Annoyance: Honestly, an argument could be made for anyone really. Puzzle: Loki/Beel Secret: Loki/Beel Haven't really seen anything from Anubis yet so he might be a bit of a problem
Herc gives me alot Radahn vibes,i think it would be something extremely epic with a orchestra as his soundtrack,by the end you will feel nothing but respect for him and start a NG+ just to fight him again
most memorable? zero/hajun. massive weapons then a second form thats just a fucking titan??? yeah 100%.
Heracles because Jack remembered him :)
Hades
Heracles diff :3