EDIT: I realize this is almost exactly opposite what I just said--I just changed my mind
I guess you will change again reading this...
you guys fully misunderstood me...
I think is better if I say my whole point of view about this...
I`m not talking about any categories. I`m talking about objectives what helps you to do something, (anything not just on a contest) and helps the judges to classify your work.
Let`s start whit the beggining, you have the contest, you could have any number/specified number of projects(my point is if you ar doing a more projects, then you can`t do as good as you could do one. The time is equal however other problems can shorten your time.), that you could present, but this way everybody have equal chance becouse only one of your projects will win, but your each projects have 100% of chance if you made it as good as you can.
Until now you have a few objectives to achieve:
efficienty creativity, and I just said one more usefullness.
Every project need to be judged by judges/public/both in case of each objectives. For example
You have a project, and you got
x points for efficienty(For avoiding misunderstandings, I advice that every participants would have to write a specification post/document/whatever... and the judges can clasify about that what is written in it if all features are done and working, then that is 100% efficient and that mean 100 point. The unspecifyed features that are made after shoud be the bonus category, and every project can get a few more point for bonus that should be decided by judges.),
y point for creativity,
z point for usefullness.
If you have got in sum more point then the other, you win.
I mean you win in your category
of course categories are good idea, but that was not what I`m talking about.