IMO all of them should be judged by a panel, its only fair that way. One persons idea of good gameplay could well be entirely different to anothers, equally valid. Also, techical might seem to be more cut-and-dry, but people have different ideas about what makes a technically good map - ie, simply the lowest r_speeds possible vs more advanced mapping techniques (func_walls to stop complex geometry splitting adjacent brushes, etc...) to lower r_speeds and maintain detail, that kind of thing. Take one of 4th's for instance - incredibly good r_speeds but a bit barren (in my opinion) compared to say ub_abbey (beta status aside!) which is more detailed but has some >1200 r_speeds dotted around.
At the least, I think each judge should give an out-of-ten rating for each category respectively, that should at least balance it out (as long as the judges feel confident being able to appraise each category!).
- Dagless