Bards are always needed and the most raid oriented of all the classes I think. The thing about a Dirge vs. Troub is that you only need one Troubador in a raid for the casters (sure two is ok) but 3 dirges and a troub seems to be the norm. If you are doing strictly PU raids I would think either class would have no problem finding a spot as they are usually not as picky as the average raid guild. Right now, I am working on my Troubador and loving it and I think that is what is important. That you enjoy playing your class. The more you like what you play, the better you will be at it. I had a friend that leveled all the way up as a Troub then betrayed to a Dirge as it was needed, but he couldn't stand it and betrayed back
Two different parts of the playing field I suppose.Good luck!