While it is true that the stringed instrument ranged is wider, and it could provide a problem by splashing ballads on to the melee, SE already pseudo-solved that problem by giving us piannismo. As long as there's only 1-2 mages in your party who need ballads, it shouldn't be hard to just target them individually. Obviously situations will vary though.
Nezea: I disagree with two points:
1) "Obviously, a string instrument is best for doing Ballad on a party consisting entirely of mages."
This was true before Mage's Ballad III came out. Now it would take serious string skill to get a radius larger than 10' from that song.
2) "The next song you cast always overwrites whichever existing one has the shortest duration."
This is also not true necessarily. Deo's example was obviously blatantly wrong unless you're using Nightingale and Troubadour, but if both songs on someone have a longer duration than the song you're currently putting on will have, then you'll get a "has no effect" message. Basically, the shortest song of the *three* is removed.
However, due to the not-so-great enhancement in duration that you get from +song on instruments, you rarely run into this because enough time passes between songs.
All of point #2 being said, thank you, SE, for Tenuto.