I'd say go with Kiki. Not because I think the outfit is necessarily better than the other, but because I personally prefer it. I don't think running into another cosplayer in the same outfit is a problem. I've done it, we took a picture together. XD
To be honest, I haven't actually seen anyone go as Kiki before. I'm sure someone has gone to AX like that, but I just didn't notice them. Either way, I don't see the problem here.
I agree that you should invest in some red flats. They shouldn't be too pricy and your feet will thank you. I also think that the cosplay isn't something to out there to be seen in public. Only the broom is. But, you won't get too many people thinking you are odd on a convention day. C: