Up first, we have...
If it isn't from Himeko, it's going in the garbage. If it is, she will slowly savor each bite as if it had been sprinkled with angel dust and kissed by a goddess, and then keep the chocolate box as a memento.
Will accept it with a little tongue-in-cheek flirtiness but only really look forward to seeing what Michiru gives her (which will no doubt be perfect).
Will raise one eyebrow and be like, "Who are you? Why are you giving me this?" and suspect you of being insincere. If it's from Shiori, she will wonder what it's laced with and attempt to forget about her again by chucking it into a pond.
Hates Valentine's Day, mostly because she hates getting chocolate from fangirls. She will refuse anyone's chocolate. Almost. She will happily eat anything Yumi gives her, even if it's filled with rusty nails.
Will politely accept it among the gajillion other gifts and love letters she gets, but will later swallow a handful of pills, wash them down with some hard liquour, and walk in the rain while thinking about how Valentine's Day chocolates will never fill the void in her heart.
Will say "Mmmmmm, chocolate!" and give you a hearty thanks. If you're Yumi, expect her to be all over you. If you're Shimako, expect her to eat your gift without realizing it's yours.
Pre-Nagisa, she would have been like "Of course I'll accept them, my little minx," and tried to remember if she'd already slept with you or not. Now that she's with Nagisa, she will be flattered, but won't reciprocate.
Will smile and accept it with a faux-surprised "Ara!" ("Oh my!"), but probably forget your name in two seconds since she only wants chocolate from Natsuki. If she uses your Valentine's Day chocolate for anything, it will be to try to make Natsuki jealous.
She isn't completely aware of how popular she is, so she will accept whatever she gets with a genuine smile of thanks without thinking too much about what it could mean. Just watch out for Wakaba. (Anthy would actually be pretty chill about it.)
Have a Happy Valentine's Day!