Brett Favre or Joe Flacco?

so basically... i have both brett and joe on my fantasy team. as you may or may not know they play each other this next week. im not really sure witch one to start. my brain tells me joe flacco because the ravens wont really run much with the vikes good run d, and the vikes p defense isnt to amazing. but my gut tells me brett because he always has the ability to have an amazing game and the last two games, the opposing qb has thrown 250+ yards against the ravens and brett has the ability to do that. what should i do?