i just went through this myself. what i was able to determine was that my intentions were most suitable to a round neck...i play slide guitar and simply wanted the resonator sound. i play with the reso upright all the time and do a great deal of fretting along with my slide so,....round neck is made for that.
if what you are interested in is a more "classic" dobro sound and intend to use a slide exclusively ( and higher , instead of lower tunings) the square neck would be the ticket.
ditto on the folks from reso-nation...very helpful!...freeman as well....most helpful and willing.
