Which free agent would you sign? Marc Gasol or LaMarcus Aldridge

— -- I think there's a two-pronged trick to succeeding in NBA free agency.

First you have to avoid the biggest pitfall of the process, which is to pay someone based on what they've already done as opposed to what they are going to do. It's easy to make the mistake because the player's track record is just that -- a matter of record. But the future, as always, is uncertain. Also, the track record matters, because that's all we have when projecting a player moving forward.

After that, even when you've arrived at an in-house projection you're comfortable with, you have to deal with the second prong: valuation. Given the scarcity, or lack thereof, of a player's future dossier and other market factors, what is that performance going to be worth?

All of this makes free agency more than a matter of "who is better?" because you not only need to find the right guy for your roster in terms of on-court fit, but you have to account for the restricted nature of a player acquisition universe governed by the salary cap and luxury tax limits.

Every dollar overspent is a dollar you can't spend on another player. With that in mind, let's begin our series of "Who's Better: Free-Agency Edition" and compare free agents with similar general profiles. In most cases, it's not difficult to identify which player is "better." Identifying which player teams should actually sign is more nuanced. We'll give it a shot.

We began this series the other day by comparing wings Jimmy Butler and Khris Middleton. Today we move on to a battle of the bigs: Marc Gasol and LaMarcus Aldridge.

Marc Gasol, C

Last team:  Memphis Grizzlies
Season-end age: 30.2
2014-15 WARP (rank): 11.7 (14)
FA status: Unrestricted Free Agent

Why Gasol's Better: These players don't play the same position. Nevertheless, they are the top two players technically to be on the market this summer and, as fellow big men who are roughly the same age, they are competing for the same offers. Theoretically anyway, as it's sounding more and more like a sure thing that Gasol will stick in Memphis and not even explore other opportunities.

Even more so than Aldridge, Gasol has a skill-based game that is a good bet to age well. His athletic factors keep increasing as he gets older because of his work ethic and recognition that he needs to maximize his innate natural gifts in order to maintain a high level of play. In fact, Gasol has posted similar ATH ratings (a metric that estimates athleticism based on statistical indicators) to Aldridge over the last three seasons. His block rate doubled that of Aldridge last season and as a former Defensive Player of the Year, his defensive RPM last season (plus-2.30) towers over Aldridge's (plus-0.67). It's Gasol's proven ability to anchor an elite defense that really gives him a leg up on Aldridge.

Gasol is a versatile offensive player, one of the best post passers in the game, and a legitimate secondary playmaker. Last season, Gasol used 5.6 percent fewer possessions than Aldridge, but still put up a career-best usage rate (24.6 percent). He did this while maintaining career norms in true shooting percentage and keeping his turnover rate down. In other words, he was asked to do more, and did so without any discernible loss of efficiency.

In addition, Gasol has shown he can team with a traditional power forward, as he has done so the past few years in Memphis with Zach Randolph. With news that he's not taking meetings with any other teams, it's likely he'll continue to do that for several years to come.

At the bottom line, over the past three years, Gasol has a six-WARP edge over Aldridge.

LaMarcus Aldridge, PF

Last team: Portland Trail Blazers
Season-end age: 29.8
2014-15 WARP (rank): 8.7 (31)
FA status: Unrestricted Free Agent

Why Aldridge is Better: Aldridge finally expanded his face-up game to the 3-point line last season. Doing so enhanced his efficiency, though his true shooting percentage remained below league average. While Aldridge doesn't have Gasol's passing skills, as a player who excels in isolation, he rarely turns the ball over. His offensive RPM (3.76) was 2.2 points better than Gasol's, and it's been higher on that end for five straight years. While Aldridge's face-up game allows him to team up with a defensive center, or even one that plays in the low post, his own low-block skills are strong enough that he can play with a floor-spacing big, as long as that player can also protect the rim.

Aldridge isn't nearly as accomplished as Gasol on the defensive end, but he's not a center. And he did play big minutes on a top-10 defensive unit last season in Portland. He has had a positive defensive RPM in every season of his career, and his numbers have only gotten stronger through his career, until last season. While he's not an elite rim protector, his defense is solid enough to justify the court time Aldridge gets as an offensive centerpiece. If he continues to hone that 3-point stroke, Aldridge should continue to provide the ideal mix of offensive versatility that teams look for in a contemporary big man.

Verdict: Gasol.

This is a tougher call than you'd expect. At first blush, it would seem to be all Gasol, but scorers of Aldridge's proficiency are few and far between. Both players will draw max offers and are in the same experience tier, so they'll have similar contracts. That means we're picking strictly on what on-court value these players will provide going forward. Their durability records are similar as well, though Aldridge tends to average a couple of more minutes per game. While Aldridge has a couple of extra NBA seasons under his belt, they're the same age, which might be a factor towards the end of their new contracts.

However, neither player relies on elite athleticism to produce, so their production should remain steady for the foreseeable future. Gasol gets the nod because of his ability to anchor a top defense. Elite defensive centers who also are featured producers on offense are really hard to find. In reality, it might come down to what your system is, and what kinds of players you have to team with these players. What would really be ideal would be to pair Gasol and Aldridge in the same frontcourt.