You can take Brady. I'll take Montana.
Let's also not forget, Montana didn't exactly go through the playoffs in that era against easy D's. He played in the era of the Redskins D. The Taylor led Giants. The Bears. The Cowboys. Etc. While the Seahawks are great now, they pale by comparison to the violent carnage that those D's put forth in that era.
I've seen both guys play. To me, Montana is the better QB. Both are HOF's. Both are in the top of all time. I just take Montana each and every time. Again, it's like Walter over Emmit Smith. Sure, Smith has more championships, yard, etc. But Walter was better. And all else equal, that's the guy I want handling the ball when it matters most. Same with Montana.