I would actually go with Favre this week because of the matchup. Brees draws the best pass D (and fifth best in terms of fantasy points allowed to QBs) and I think the Saints will have a bit of a letdown this week. That said, I think you have a baseline of 250 yards/2 TDs from both guys, so you really can't go wrong.
As for your flex, I think Jackson (if starting for sure) has the best opportunity for guaranteed points and solid production against a Jets team that hasn't been as good against the run as you might think. If Jackson doesn't start for some strange reason, I'd probably roll the dice and go with Austin - hope this helps