I know it may be terrible to contemplate, but, y'know, Jimmy Rollins and Jose Reyes are both staring at free agency. Who would you want? Of course it all boils down to "what does each cost?", but it's an interesting thought experiment. The LOLMets are in serious, serious trouble, and if the Wilpons keep the team, it may be in a financially hamstrung (if not crippled) condition for years to come . The Mets may not be able to keep Reyes (and might not want to anyway).
 LOLMets -- I have enjoyed the Phillies beating you down over the last several years, but this is just bad for baseball - I honestly feel terrible for fans, especially kids, who have no idea what this is all about and why it should impact the baseball team they cheer for.
Anyhow, let's skip past the cut to compare the two players. Then we can all play fantasy GM.
As the season starts, Rollins is 32 and Reyes is 27. That is the first and most obvious difference between the two. How will Rollins' game look when he is 36 or 37? Do you want to sign him for 4 or 5 years for a spot in the middle of the infield? Reyes has not been free from injury, but he has fewer miles on him and is presumably in his offensive prime.
Reyes' best defensive days are probably behind him (same for Rollins, too, of course). Rollins defense appears to have peaked during his 25 - 28 year ages, when he was good for dWAR of about 1.1 per year, per BR. Reyes' dWAR peaked at a similar average when 23-24, but it is now hovering at 0.0/slightly negative for the last three years, including the last two seasons where Reyes missed significant time because of injury/illness.
Offensively, the stolen base percentage of Reyes puts him in territory that makes the SB more or less a wash, so his large absolute numbers of SB are offset by the runs he costs his team when he gets thrown out. A success rate of roughly 75% is the "magic" number. That obviously excludes a game analysis where a particular SB at a high leverage moment may be worth much more than an inconsequential CS. Nevertheless, the percentage "rule of thumb" is useful to consider. Rollins' stolen bases are nearly all gravy (17 SB and 1 CS last year).
Reyes has traditionally exceeded the .330 OBP generally considered to be "average" for MLB. Reyes fell to .321 last year, but that was his worst OBP year of the last 5. All 4 prior years, he exceeded .350, which is very good. Reyes has achieved this outcome as a result of a higher batting average than Rollins as well as walking more often, though perhaps Rollins learned to walk more last year. The 40 walks Rollins worked in 2010 in roughly a half season may have helped him to reach a career high if he had played a full season. Even so, Reyes walks more, and has a much better track record of doing so.
Rollins' average, never great, has declined each year since 2007, to a career low of .243 last season. His SLG was a career low of .374. Also troubling is that his SLG has declined each year since 2007 as well. Reyes, on the other hand, had a sub-par year, but his average, SLG and the resulting OPS were all at or near his career norms. He appeared to round back into shape as the year went on in 2010 as well. His OPS bottomed out at .536 OPS on May 19, bouncing back to .749 by the end of the year.
Rollins is aging and getting worse. Rollins suffered an injury last year, sure, but increased injury risk is a consequence of age. Aside from the MVP year, Rollins has never exceeded a WAR of 5.0. Reyes did it for 3 consecutive years, until his health issues ended the streak in 2009.
Bottom line? Reyes is a better player. Reyes has been a better player. Reyes is likely to be a better player as both players get older. This is not shocking, or surprising.
What should the Phillies do to fill the hole at SS in the next 3 - 5 years? Depending on how this year shapes up for him, Reyes may be able to get a 6 year/$100MM-ish contract. I figure he may be worth 3.0 - 3.5 WAR per year, even if you figure that he slows some as he gets older. His game is not just his legs -- he has power and he gets on base at an above-average rate, all while playing a premium defensive position reasonably well.
That said, the Phillies probably cannot afford $16MM/year given their current payroll, but after this year, the decks clear a bit. They also have to pay *someone* to play at shortstop. It is also reasonable to start asking whether Jimmy Rollins should be that person.
If Rollins is healthy, is it realistic to expect him to put up more than 2.0 WAR regularly for the next 3 - 4 years? That's an "average" MLB starter. The Orioles got JJ Hardy for about $6MM and his numbers (OPS and WAR) were similar to Rollins last year (but in more games). Rollins > Hardy, but not by so much that they can afford to overpay him, especially in a multi-year deal. If Rollins is healthy, he surely performs better, but there's no guarantee he will be healthy. Even when healthy, his decline from the MVP season has been obvious. Of course, the Phillies have no obvious replacement for Rollins waiting in the wings, and signing a free agent (Reyes) is an expensive way to build a team, in terms of purchasing WAR on the open market and losing picks.
Could Rollins be signed for 3 years in the neighborhood of $12MM/year? Would you want to? I am less and less sure that I would, if I were the Phillies. Of course, if the Phillies don't sign Rollins, who does play SS for them? This is not a pretty picture.