Carl Crawford is the best free-agent-to-be on the Rays, but the team with the best record in the bigs may have a harder time replacing Carlos Pena.

Since joining the Rays in 2007, Pena has been one of the major league’s most prolific power hitters. He’s hit 143 home runs and driven in 404 RBIs in that span, and led the AL in homers in 2009 despite missing the majority of September with two broken fingers.

Pena is also one of the league’s better defensive first baseman, and won a Gold Glove in 2008.

But the other facets of Pena’s game – most noticeably his ability to get on base – have been in steep decline.  Pena’s batting average has fallen from .282 in 2007, to .247 in 2008, .227 in 2009, and a career-low .198 in 2010.

Advanced statistics suggest that luck has played a big part in his embarrassing average this season, but such a steady four-year regression means that Pena’s best days as a hitter are clearly behind him.

In addition to his declining numbers, Pena must also face a fairly stacked class of free agent first basemen. Big name players such as Adam Dunn, Derrek Lee and Paul Konerko are all set to become free agents after the season, as are complimentary players such as Lyle Overbay, Jorge Cantu and possibly Lance Berkman.

Competition aside, Pena still excels at preventing runs with his defense and driving them in with his power, and several teams will be in the market for his services this winter. Seven teams who could have interest in acquiring Pena are:

Texas Rangers: Cantu and rookie first baseman Mitch Moreland have performed competently for Texas in the second half of the season, but Pena would provide a significant upgrade over both. It’s not hard to see Pena regaining his 30+ home run form in Rangers Ballpark in Arlington, and Texas’ stacked lineup would allow him to bat near the bottom of the order.

Seattle Mariners: The Mariners have hit the second fewest home runs of any team in the majors, and could certainly use a thumper like Pena to bat fifth or sixth in their lineup. Justin Smoak is the team’s long-term answer at first base, but they could have interest in adding Pena on a one-year deal.;

Washington Nationals: The Nationals are working on a long-term deal for their incumbent first baseman, Dunn, but aside from Crawford, the 30-year-old Dunn is likely to be the most sought-after free agent batter on the market this offseason. Pena can’t match Dunn’s ability to reach base, but he’s far better defensively, and is the best bet to replace Dunn’s huge power as well.

Toronto Blue Jays: The Blue Jays love their power hitters, and Pena certainly provides an upgrade over Overbay in that category. After trading away Brett Wallace to the Astros, the Jays have no long-term answer at first, and could offer Pena a multi-year deal.

Chicago Cubs: The Cubs may have some interest in bringing back Lee, who they traded to Atlanta early in the season. But if Lee goes elsewhere, Pena could be the left-handed power bat the Cubs have sorely lacked over the past few seasons.

Chicago White Sox: Current first baseman Paul Konerko is still very productive and a fan favorite, so the odds are good that Kenny Williams and Co. will find a way to bring him back for his 13th season as a White Sox. Chicago lacks any internal options should Konerko leave, though, and Pena would be a logical replacement.

Boston Red Sox: Odds are Red Sox fans wouldn’t react favorably to a Pena acquisition, but if Adrian Beltre leaves via free agency, it’s a real possibility. The Sox could move Kevin Youkilis across the diamond to third, sign Pena to a one-year deal, and then go after Adrian Gonzalez or Albert Pujols the following offseason.

Although the consensus is that they won’t be able to afford him, perhaps the best fit for Pena is a return to the Rays. As deep and talented as their farm system is, the Rays lack any intriguing first base prospects, and cannot replace Pena the way they can replace Crawford with Desmond Jennings. And while Pena might have to take a slight pay cut from the more than $10 million he made in 2010, the Rays may be one of the few teams willing to offer him multi-year security.

The days of Pena being one of the preeminent first baseman in the American League are likely over, but he’s still a valuable major league player.

And unless they sign a different free agent first baseman, he’s a player the Rays are ill-equipped to replace.