Broadway, because great musicians are better suited to bombing.
Assume your tourism output is +100 (not unreasonable at that stage of the game with theming bonuses and dig sites if you're serious about a cultural victory), that means your bomb is worth 1000.
That means your +2 per turn great musician will produce more tourism than his bomb in 500 turns. Even if you have max bonuses (+75%) you will only get +3.5 out of him a turn which he will produce in 285 turns. It's seriously not worth it, the bomb is nearly always better.
That's without accounting for the fact that the bomb will often bump up your influence level over a civ which will increase your ideology pressure and reduce their happiness (or increase your happiness if they have pressure over you).
You're missing some numbers there. The three Great Works of Music will each be producing 2 tourism per turn (3 with a Hotel, then 4 with an Airport, then 6 with the Visitor Center), but you'll also be getting 6 from the theming bonus (12 as France). You might get another +50% on top of all that from World Religion, and as much as +68% from ideology. +100% with International Games, +100% during a Golden Age as Brazil. And then up to 75% on top of that. And another +100% with the Internet, eventually.
Conservatively, let's say you've just got a Hotel, you're not France or Brazil, you don't have the International Games bonus, you don't have the World Religion, and you're only getting +34% from ideology (you went Freedom). That's 15 for the Great Works plus the theming bonus, or 5 tourism per turn for each Great Work. Let's fudge the numbers, just to make it simple, and say that your average bonus for religion/trade routes/open borders is 66% (I admit this is a little high). That means each Great Work is producing 10 tourism per turn.
If you have seven opponents (Standard map), that's 70 per turn. The Great Musician will deliver 1000 to only one civ; the rest will get 200, for a total of 2200, so a Great Work will outproduce a Concert Tour in 32 turns.
Now it's true that the Great Musician allows you to direct that tourism where it's needed most, whereas the Great Works will be wasting some on civs you're already dominating, but they'll also make later Concert Tours stronger. The Great Works will produce more and more as the game continues and you add bonuses; in the Information era, with the Visitor Center and the Internet, you'll get about 25 tourism per Great Work per turn. In an extreme situation, as France or Brazil with both Order bonuses working, you could get almost 60 tourism per turn from each Great Work. This means that a Concert Tour at that point in the game will be worth an extra 750-1800 tourism just from the three Great Works in Broadway (on top of all the tourism the Great Works generated in the intervening turns).
tl;dr: it's better to fill Broadway than to use those Musicians for Concert Tours unless you're already dominating most of your opponents and are relatively close to dominating the last 1-3.
