I will be frank with you.
I main Nero because he can spam birds (before Cadenza)
His range is also quite large and insane.
my second is Nanaya Shiki
third is Red Akiha / Kohaku
----
The reason why I like Nanaya Shiki is without a doubt, or arcade mode I can spam his moves quite desperately, making him a very lethal choice against skilled players even when I am not a skilled player myself. I have defeated a few people on /jp/ online plays (regulars at that) so I know what I am talking about. My only loss? I am not so fast as to be able to pull off 16 hit combos (which is possible)
With Akiha's shoulder bump and combos, I can pretty much says she is better than Kohaku is you do air rage combos. Akiha is fast, easy to use and has knockback on almost every single attack. Plus her light punch is fun to use and has a longer range (what I observed).
Kohaku is awesome, her range is insane, her speed as well, they made it harder to summon the spinning tree in the arcade version, but on PC mode, I normally main her. Her potion throw while mid-air carries quite an insane damage even when the damage level is set to smallest.
Kohaku has quite a number of tricks up her sleeve that makes her quite impossibly one of spammiest characters if it were back in Re-Act. Why? Cactus > punch > hard > lift > potion throw mid air, 7000 damage when set to highest.
Ciel is no more fun for me since Actress Again, I find her moveset terrible.