The most important position is starting pitcher. Those clowns who claim that a pitcher shouldn't be eligible to win MVP because hey don't play every day have a fundamental comprehension problem when it comes to the game of baseball. Pitching isn't everything, but on the list of the top 5 most important things in baseball, it's numbers 1, 2, 3, and 4.
The Red Sox allowed the fewest runs in baseball last year, a poultry 4.1 per game. In the playoffs, the Sox allowed 3.3 runs per game. And that's why they won it all. It wasn't Ellsbury's "excitement" or David Ortiz's "clutchness" or even Mike Lowell's stability. It was good, solid pitching.
Starting pitching is also the biggest reason why the Red Sox bullpen was statistically the best in baseball. The bullpen wasn't deep last year. Apart from Papelbon, Okajima, and Timlin; it was a crapshoot. But with good starters going deep into games, mediocre arms like Javier Lopez's were kept relatively unexposed.
This year's rotation has more question marks than Matthew Lesko's jacket.

Who will be the #5 starter? What will the Sox get from Colon? When will Schilling return and what will he give the team? How will Daisuke pitch now that he's had a year to adjust to America? How will young guys like Lester and Bucholz perform? How will Wakefield's back hold up? And the latest question: When will Beckett be ready to go?
Despite the recent back spasms, Beckett is the most reliable and undoubtedly the best pitcher in the rotation. he's an Ace, a bona fide Ace. He was the only 20 game winner in the Majors in '07, was 6th in the AL in ERA at 3.27, was 7th in strikeouts with 194, was 6th in WHIP at 1.14, and should have won the Cy Young.
His post-season numbers were even more impressive. In 4 starts, he went 4-0 with 30 innings (7.5 per start), 4 earned runs (1.20 ERA), 19 hits, 2 walks (0.70 WHIP, which is absurd), and 35 strikeouts (10.5 K per 9 IP). Just to put things in perspective, Erik Bedard led the AL in strikeout to walk ratio with 10.93 to 1. Beckett's K/BB ratio in the post-season was 17.5 to 1.