Who starts Opening Day isn't really all that important when you think about it. Rotations get shuffled and reordered throughout the season. And who starts Game #1 in April isn't nearly as important as who starts Playoff Game #1 in October (or Game #163 in October). The only reason it's interesting to me is because the Red Sox don't have a true Ace.
Justin Verlander is starting for Detroit on April 5th. The Tigers didn't need a press release to tell us that. He'll be facing Jon Lester. Lester was last year's Opening Day starter. So Bobby Valentine's first managerial decision in a meaningful game shouldn't be too controversial.
Why Lester over Beckett? I think Lester's more consistent. Beckett also suggested to Valentine back in January that Lester start Opening Day. To be honest I don't think Bobby V deliberated much on the decision. Neither starter is an Ace. Lester is a consistent #2, and Beckett fluctuates between 1, 2, and 3, averaging out to another #2.
I'm really anticipating the start of the season. Much like I anticipate dentist appointments. You're worried that it might be painful. There's a slim hope it won't be. Either way you just want it to happen so you can get it over with.