For me, my signature characters aren't the ones I spend the most time on but the ones I have the most connection to.
Blueside: Angel Red - Kin/Arch Defender, was my very first character on Legacy and the first one to 50 on multiple servers. Alluding to another thread, despite her name, she is not an angel but is half-dragon.
Redside: Hemorrhagic Fever - Water/Poison Corruptor, my second 50 on HC and is tied with 1st place on the most fun to play. It is truly vile and deserved of all it's villainhood. Its creation precedes the pandemic, but I've avoided playing it since that kicked up for obvious reasons.
Goldside: Burnished Dragon - MA/Nin Stalker, she escaped New Tokyo and made her way to Praetoria City where she joined the Resistance, secretly working within the Tyrant's regime to mitigate their insidious destruction of humanity's free will in their "utopian society".