my crowntail female was the sweetest girl i'd met at the time. she never flared, not even at another betta. i really miss that girl. she was so cute. tiny, curious about everything, sweet. ever water change was an adventure for her, after i upgraded her to her 2 gallon. she'd swim around for hours, exploring everything, even though none of the decor was different, things were just rearranged.
also, i don't know about CTs being most aggressive, either. my CT, Zidane, is the shyest betta i've ever met. his tactic is to run, then come back and flare, then run again. he's always hiding in his bowl, under his bubble nest(note: the bowl, is his cave. :3 he nests in it all the time!).