It is all about your start, and what your initial plan is. Mining has to be one of them because getting BW early to chop and/or whip is so critical. Then your best bet is probably Agriculture because you are nost likely going to be able to help your growth with an early farm. But if you are on the Coast next to clams/fish/crabs you would rather have Fishing. If you plan to discover early religions, perhaps with an eye to a cultural victory, or early shrine, you would love to have Mysticism and try for Hindu/Buddism. Mostly I find I can found later religions and count on others to spread early ones enough where founding an early religion is not that big a deal, at least as far as getting the prerequisite 3 religions in your civ for an attempt at a cultural win. You can also argue Hunting for the early Scout. This varies a lot on your luck with huts and the surroundings. I do appreciate it a lot when I play Darius, but I like to start with a worker and sometimes he can get left with nothing useful to do to start the game.