When going for cultural victory, I plant most of them for great works early on in the game, then tend to use the special ability more and more the later the game goes. The bonuses you get from them are a lot larger later on, and +2 culture/tourism at that point is a relatively small effect. If you're playing Brazil, you'll especially want to use artists for golden age, since it doubles your tourism as well. Musicians are best used in the late game for concert tours on whichever civ is the leader in culture, and your tourism output is already high, so the concert tour is a lot stronger. Writers are the only one I might create a great work from late in the game, though I generally get more from the big culture boost that lets me snag another policy/tenet instead.
When not going for culture victory, I'll plant musicians and writers early on. You get more culture in the long run from +2 multiplied over 150-200 turns of remaining gameplay than you get from spending the writer on a "culture bomb", and early concert tours are pointless since your tourism generation will be so low. I might plant an artist or two, but tend to use most of them for golden ages instead.