This one is even harder than yesterday's, because I can look at my own characters with an eye toward how I experienced them, but with someone else's character...especially if they were your fellow player in a game ran by a third party, there's that level of distraction, where you're planning your own actions, looking forward to your time to act, and keeping up with what the GM and any number of other players at the table are doing, and I think sometimes those characters can get lost.
That's not to say that Taylor's "Dr. Robscar" (I forget his actual name now), a Camarilla vampire forcibly turned Sabbat that killed my first character in the same campaign and ended up blowing up some of the Primogen Council before skipping town, or Tony's Cleric in Paul's Gnomad game aren't awesome, but I tend to realize how awesome characters are more when I'm watching them from the point of view of a GM.
There have been many exciting and intriguing characters throughout my GMing years, and the characters in my current Defenders D&D game are shaping up to be amongst the 'cool kids', but one character from all the way back to the first game I ever ran stays firmly in my mind,.
Damion Flair was a homicidal Camarilla Malkavian (with randomly generated Multiple Personality Disorder as his mental flaw) that perhaps would have been better suited to the brutal mindset of the Sabbat. Embraced in his cell at a penal mental institution and broken out by his sire after his cold body was taken to the morgue, Damion was turned loose with no guidance and rapidly fell back into his murderous ways, except with the Curse of Malkav adding to his dementia.
Damion often killed to get what he wanted, and sometimes would return to his old asylum as a sometimes-haven and feeding ground, which John D. always made seem like a trigger for him, whereafter he would be more violent and off-kilter than usual. The most memorable of these episodes came after one of Damion's acquaintances got staked and baked and he felt like he had been flushed from the asylum, his usual hidey-hole, he stalked and Dominated his way into a condo and killed the 5-member family therein, sitting them on the couch with the tv playing at most hours, letting them rot in their AC-blasted living room as he lived a workaday life around them, talking to them about "work" and what have you for multiple sessions.
It was probably some of the best roleplay I have ever seen, even to this day. John D. had a way with characterization that made his penchant for beater-archetypes never dull and I wish he still had time to commit to gaming.