I always liked the idea of being able to use powers that hide in plain sight. I think Bard's magical songs have a lot of potential behind them for that. Not to mention, I've just always wanted to learn a string instrument and haven't much time for it.
Bards can be really dangerous if unexpected.
Picture it: You're at the bar, sitting at the counter. You've been talking with the bartender about the goings-on that day while a hooded figure sits behind you in the center of the tavern amidst an eager crowd of listeners. You and the bartender had got on the subject of his finely aged drinks. He has a special wine that has been aged far longer than any other in his inventory, dating back to when his father taught him the value of aging wine. It was a very expensive drink, secured away in the back in the hopes that a noble would want to buy it. It was then you noticed that none of the once noisy patrons had been talking. No laughing, no cheering, just listening to the bard play his suggestive song, surrounded by a ring of coins that they had tipped him with throughout the day. The bartender noted how strange it was, but you brushed it off, figuring they just enjoyed the peaceful music, and not being one to complain about the atmosphere. You had been drowning out the music to hold the conversation, but once you noticed its melody, you were enthralled by it. It gave you a sense of calm serenity you hadn’t felt since sometime before your travels. You consider giving a tip for your new-found mood but pull back when you realize any flexible income you had before coming in was lost to the mug in your hand. The bard notices your rustling bag and frowns at its retreat. The bard begins to play a new song. The hypnotic pattern combined with the alcohol swirls your mind, along with everyone else’s. With a blur of speed, the bard uses his improvisation skills to whip out dinner knives, one for you, and one for the bartender. In your daze, a sharp burning enters your throat as you fall over. The bartender is heard, falling face-first onto the counter as the bard smiles and grabs your coins. He runs to the back room and finds the wine the bartender talked about. The patrons dashed after him when they came to their senses, but in the minute it took for them to respond, he had already changed tunes, and snuck, transparent as the wind.
For me personally, though, I think the idea of teleporting magic via guitar riff is a fun way to save on gas when traveling.