If you are powergaming, there are better alternatives than a Bard. For example, you can run a party with powerful specialized characters instead of a party that includes a "jack-of-all-trades-but-master-of-none".
On the other hand, if you are roleplaying and want to play a Bard, then there is literally no substitute. Bards are sort of like Druids to me in that respect. A powergamer might choose a Druid because of the availability of a few special skills or abilities that are not available to other classes, but the best reason for playing a Druid is that you want to play one. Same with Bards.
Mages, Fighters, and Thieves are a lot of fun to play, but when it comes to roleplaying, they are blank slates. Aside from their generalized skills, they don't give you a lot of cues about who they are or what sort of background they have. And chances are, when it comes to a game like this, most people don't think much about their characters' backgrounds, which is why the story provided by the designers (child of Bhaal raised by monks in fortified library) is not only sufficient but also compelling, and there's nothing more to add. But when you play a Bard (or a Druid), you can make many assumptions about his or her background based on what you know about the rich traditions of Bards (or Druids). So automatically, you are thinking about character traits and not just abilities. If his or her abilities do not satisfy you, or if you do not care much about character traits, then you are better off with a powergaming character.
I know I've said this a hundred times before, but I once played with a party of troubadours, and it was one of the best roleplaying experiences I've ever had. I was doing a lot more than thinking about ways to kill monsters and gain experience; I was thinking about WHY they did the things they did and how they fit in with the world around them. For example, why would a character participate in a guild war, above and beyond the player's need to progress to the next chapter in the game? I gave a great deal of thought to questions like that, and it made the game world come alive, despite the inherent shallowness and self-contradictory nature of the main plot. (I realized just how shallow and self-contradictory it is BECAUSE I thought about it instead of merely taking it for granted and saying, "Okay, whatever, where do I find some monsters and treasure?")
My party of troubadours was carefully constructed. I started with the idea of an all-bard party, but I also let the story inform my choices. For example, I had to include Imoen because she has a significant relationship with the main character. And there wasn't any reason why I couldn't hand her a tambourine.
My characters also had a natural interest in the playhouse (and as a player, I had an interest in the stronghold quest), and it was only natural to include Haer'Dalis, whose script involves a subplot with Aerie, who also has a background as a performer from her days in the circus. So I had a party consisting of a two Blades, a Skald, a Jester, Imoen, and Aerie, which was pretty cool. The absence of a strong melee character early in the game proved to be very frustrating, especially before they all acquired Stoneskin. (When you have several spellcasters in your party, it's not easy to find enough spell scrolls for all of them.) Yes, I had to do a lot of micromanaging to keep them buffed and ready for battle. But it was a lot of fun to experiment with creative strategies and little-used abilities such as bard songs. It was one of my most memorable adventures.
