I can counter with you all day long. You didn't compare home runs but you compare steals, you didn't talk about fielding, and hopefully you don't think Aybar is a better fielder. Now you say you will have Aybar for 4 years instead of 2 for JJ. That just totally goes against your feeling of getting Manny to shortstop which is well documented.
We can go on even more if you like.
Aybar has had a UZR
of -2.2, 1.2, -2, 4.5 and 5.5 over the last five years.
Hardy has had a UZR of 11.4, 10.7, 8.1, 6.8, and 6.5 over the same period.
UZR suggests they aren't even close on that front, with Hardy's defense worth roughly 8 runs over the course of the season compared to Aybar.
In defensive runs saved above average, according to baseball info solutions...
Aybar has saved 3, -1, 4, 1 and 0 runs over the last five seasons.
Hardy has saved 18, 8, -5, 2 and 13 runs over the last five season.
Once again, this stat doesn't think it's particularly close, with Hardy's defense being worth something like 10 runs over the course of the year over Aybar.
So, that's definitely something in Hardy's favor in a comparison with Aybar (though you should of course keep in mind that defensive value is a component of WAR, so you can't just say "well they may have similar WARs but Hardy's much better at defense so I'll take him).
For Hardy to be that much better at defense with the two players still having comparable overall value (that's what WAR measures, don't let the acronym throw you off), he'd have to be much worse at some combination of offense and baserunning.
For hitting, let's look at wRC+. Again, don't let the stupid acronym fool you. Here's what it does: it measures the runs each player accounts for per plate appearance-- adjusted for ballpark factors and the run scoring environment of the league they play in-- and is presented where 100 is average, and each number above or below is a percentage above or below average.
Hardy has had a wRC+ in the last five years of 78 (22 percent worse than the average hitter), 113 (13 percent better than the avg hitter, etc.), 101, 94, and 67. As a SS, he can be a worthwhile offensive contributor even while being below average, so obviously he was quite valuable two years ago.
Again, those numbers: 78, 113, 101, 94 and 67.
Aybar over the period: 106, 106, 78, 105, and 86.
So Hardy has had the best year out of the two players, but also the worst year. Aybar has more consistently been right around a league average hitter.
But baserunning is part of how teams score runs as well, so we can't just pretend it doesn't exist.
In that realm, it's not even close.
Let's look at Fangraph's BsR, which counts not only steals and caught stealings but also how often a player can take an extra base. Again this is presented in total runs scored above the average player over the course of the season.
Hardy: 0.4, -0.8, 0.2, -0.6, -1.8
Aybar: 5.1, 4.4, 4.8, 2.1, 1.9
That's a pretty sizable difference. Not something to blithely ignore as "just baserunning." He's wroth something like 4 runs a year over the course of the season over Hardy just on the basepaths.
In the end, I'd say they're very similar players. Hardy is substantially better at defense, Aybar is slightly better at the plate, and Aybar is substantially better running the bases. Aybar is also two years younger and is under contract for two additional seasons.
Prefer whichever player you'd like based on this information-- they're close enough that you could certainly make a case for either one and be considered an eminently reasonable person. It certainly isn't absurd to think Aybar is more valuable though... especially when you consider his age and contract situation. (Aybar will be paid $8.5 million each season until he reaches free agency after 2016. Hardy will be paid $7 million in each of the next two years and will be a free agent in 2015).