What are the trends that today's music composition contests favor?

It all depends on the parameters of the competition and on who the judges are, Some competitions specifically ask for electronic music, others specifically exclude it, If it's competition for ballet music then the ability to dance to it is a big factor. As to judges often you don't know who's judging the competition, even when a big name is listed as a judge there will also sometimes be an assistent who helps vet scores before they get to that person. The best thing to do is to compose the piece you can and realize that by nature of it being a competition you're probably going to lose more than you win.

Also don't try to over-compose a piece just for a competition. Some people think that they have to go an extra step further to really concretely justify every-note, or put in a 7 voice fugue or other overly elaborate things that just look contrived to a judge. You're better off creating the kind of music you know you want to hear.

The more judges there are the more mainstream the winner tends to be. One judge may not like pop influence and discard all the scores with pop influence, another judge may not like new complexity or total serialism and throw out all those scores, and so on until all that's left is middle-of-the-road-take-no-risks music. This is true of most of the winners of the Grawemayer which has three rounds of judging and a total of 9 different judges.

http://grawemeyer.org/music/previous-winners

You may also find the winners list of the Prix de Rome informative:

http://en.wikipedia.org/wiki/Prix_de_Rome#Winners_...