I love Eileen for her honour, honesty and courage. Her spiky awkward attitude is the flip side. She's committed to Derek, Jenny, Edward and (only for Jenny's sake), Paul. Eileen sees the disadvantages of magic and is not afraid to criticize her own sake. She sees her royal status as something to be used to help other people rather than to advance herself. She loathes evil. She is incorruptible. She sees through flim-flam, which is why she never got on with Brankaresh. The fact she is prepared to follow her heart and principles by going to earth and turning her back on all she's known takes great courage. It would've been far easier to dump Derek and stay in the magical realm. Indeed the Fairy Queen would have richly rewarded Eileen for doing that.
Jennifer (but known to everyone other than Eileen as Jenny)
I love Jenny for being prepared to stand up to her mother, which many in the magical world would not do. Jenny doesn't abandon Eileen after the latter's devastating revelation as to what she is despite the girl realizing immediately the fallout from this story is going to hit her hard. Jenny was tempted to do otherwise though, realizing it would be easier for her to dump her mother. Indeed if Jenny wanted to keep her comfortable life the way it was, dumping Eileen was the only way to achieve that. Jenny knows her own mind (can't think where she gets that from! well actually I can!) and marries a man she loves, like her mother did, despite Eilen taking an instant dislike to Paul. Jenny recognizes no man would have been good enough for her in Eileen's eyes. Later as Jenny comes to terms with her new status as a half-fairy, she finds her own way of using the magic she's inherited in her blood from Eileen (and the magic she studies) and the other magic given to her by the dying fairy, Rose. Jenny certainly does not do anything simply because her mother says she should.