I would go with the 2x4 because I think the dimensions work better. You can happily grow two decent sized, or three girls if at least one or two of them are moderately small sized. My first indoor grow was in a 2x4, and it worked very well with one full sized (Mephisto Cosmic Queen) and two smaller (Mephisto 24 Carat).
The problem with the 32x32 is that 32" is not enough to house two full sized plants, at least not easily, so making efficient use of that foot print is not easy. Mind you, I have never tried it.
IMO, the real choices are 2x2 for one plant, or a fine time trying to fit more than one, a 2x4 as discussed above, or a 4x4, which is just two 2x4's together, with the same advantages of the 2x4 in terms of how plants fit. Just my take on the issue though, I expect others may differ. Good luck with your decision.