[Bryce2471]

As advice for January I have to recommend using a WCD or similar skid steer drive. So if your team has not explored these thoroughly, you should start there.

However, choosing between a butterfly and swerve drive as an off season project is a completely different matter. The swerve drive is by far the better option, for many of the same reasons that it should not be used in most FRC games. Swerve drives are expensive, difficult to design, difficult to machine, difficult to assemble, difficult to program, difficult to maintain, and difficult to drive well. But when you get it all right, Swerve drive is an amazing sight to behold. This means that when you get done building a good swerve platform, your team will have grown and learned in every way, and you'll have a killer demonstration bot.
(Just my two biased cents)

P.S. I am biased because a swerve drive robot sparked huge inspiration in me as a freshman.