well the MOST requested classes would have to be Minstrel/Rune-Keeper as they both have healing aspects to their classes (mistrels are 90% healing class and Rune-Keeper is 50% healing 50% DPS), and a Healer is ALWAYS needed in a group. BUT the downside to this is that they are both hard to train. Especially Minstrels. They also start out as weak classes in terms of armor, as both Minstrels and Rune-Keepers wear light armor (at the start of the game that is). Minstrels have the ability to wear medium-armor once they complete a class quest, but not RK's.
What i would personally do is try out ALL the classes and see which one you like best in the game. That's exactly what I did. I found out I excell at being a LM (Lore-Master/Loremaster). My secondary pick for class would be either Rune-Keeper or Hunter.
But again, i CANNOT stress how important it is to find your place in the game, specifically a place you like. Because being a game, its ALL about having fun.
Also, my view is STRICTLY limited to the Windfola server and also I can't speak for most of the stuff that happens during the beggining of the game through the middle. (I've got 3 characters I play on Windfola and they're all in the 35 - 60 range).
But again, like i said earliier, just try out the different classes and pick the one you like the best, its the BEST way to enjoy the game.