Well from what I've read/seen over the weekend, it seems that Lucina will be a solid character. From the footage that I saw, she and Marth appear to be about equally as fast, with some of their aerials lacking landing lag (I believe FAir and UAir). She is a true clone of Marth; they even share the same alternate specials. Her attacks do slightly (almost negligible) more damage than Marth's non-tipper attacks. And spacing, though obviously still important, does not seem to be as central a factor in playing Lucina as it does Marth, since damage is equally distributed throughout the sword. Overall I personally see her having a more aggro/beatdown/close style of play that is a foil to Marth's distant spacing approach, and as of right now I would say Marth has the edge, but just barely.