I definitely prefer more episodes. I've never seen a show that benefited from less episodes. The only reason to make less episodes is so that the people making it spend less money. The Flash didn't have one stinker last season, and that was at 23 episodes. My biggest hope for American TV is that it doesn't copy england and have a puny amount of episodes as a norm. When you have to wait a year between seasons of a show, small seasons are a horrible idea, and I haven't seen them work to the advantage of any show. I've seen 13 episode seasons that were mostly junk (Doctor Who Series 8) and 23 episode seasons that were spectacular (The Flash).
Now, not all 13 episode seasons are bad, far from it, but even the very good ones would benefit from a full 22-26 episode run. I have no idea why anyone would want less of a show they like, but luckily most of the shows I like won't be reducing episodes anytime soon. As for Supergirl, if it does well I can easily seen them ordering more episodes, and if it makes it to Season 2 I bet it will be a full season.