I like them both.
Lucifer is a beautiful name, but I would not use it because of the overly negative association with the ultimate evil of the Judeo-Christian mythology. Pity, really, because I really like it.
I *adore* the name
Lucius. It's very handsome and elegant, but it's also cool. It's ancient, but it also has a contemporary feel to it.
I also like
Lucian, but
Lucius is my favourite out of the three.