Well, I'd have to go for a modified Okatana. Instead of the standard curve it would just have a straight blade, still single edged.
My reasons? Well, drawing and sheathing would be made slightly simpler, and fit more towards my favorite sword style, Iaijutsu, and with the lengthened blade my reach would be longer. I'd be able to use one hand, obviously, making dual weilding plausible as long as I can train in it.
Mainly, I'd take about any variation of a Katana, so long as it was straight edge.
That or a Katana/Rapier combo
the elegance of the hilt of a rapier with the light, destructive force of a katana.