if i pick Ravens, i'm guaranteed to "win" the playoffs on the board this year (we've all done mighty well), so that's the best strategic pick. but i'll try not to be a wanker, and look at the game itself.
based on stat comparisons, i like the 49ers better. but the Ravens have a better turf record (and have played there more games). against common opponents, they both beat the Patriots, by a similar (average) margin, so the deciding team is the New York Giants, whom Baltimore beat and San Francisco got drubbed by. they've both done well in the playoffs (obviously), but i was more impressed by the Ravens' last two opponents going into their games than i was the Forty Niners' -- enough to pick against Baltimore both times (the opposite of San Fran), and thus to be more impressed by their victories. so they have the "momentum" edge if such a thing can exist.
in that vein, San Francisco's defense was more dominant during the regular season, but Baltimore's has struck me as more smothering during the playoffs, remembering that 14 of Denver's 35 points against them came from special teams, which is damn difficult for anybody to reproduce.
there's also the factor that i regularly pick against Baltimore in these threads, this year being no exception. it's nothing personal; i just happen to think their playoff opponents are better, and am often proven wrong. this year especially, i've eaten plenty of crow (or rather, crow's cousin has eaten me!). so not wanting to get burnt thrice in a row would also incline me to pick the black birds.
but i still have 2 hours left, so a pick can wait. :P