A couple of pieces of advice:
If you're caught choosing between outfield grandstand or bleachers, go with the bleachers. At least you'll be facing home plate and won't have to worry about the possibility of obstructed views.
In regards to online broker or scalper, I usually go scalper. Back when I was in college, we used to go down to Fenway and wait until the game started. At that point, scalpers are scrambling to dump tickets and you can get them at face or, oftentimes, below face. Even before the game, scalpers can usually be a better bet than an online broker, however, that depends on opponent and time. If its a weeknight game in April/May against Toronto, that's more advantageous than a Sat. afternoon game against the Yankees