I have been wondering since the game ended if Tom Coughlin should have gone for an onside kick. I have run some numbers and I believe not going for the onside kick was a mistake in this situation. There was a little over 2 and a half minutes remaining and the Giants had 2 timeouts left. Let's examine the options after the jump.
Option 1: Kick long and get a 3 and out using the 2 timeouts plus the 2 minute warning to force a punt. Eli will get the ball with a little less than two minutes left and no timeouts. I found some data over at Stampede Blue compiled between 2001-2009 which showed that defenses forced a 3 and out 34.5% of the time. So the odds of success are not good.
Option 2: Onside kick and 20%(based on statistics when an onside kick is expected) chance to recover and get the ball at your own 45 with 2 timeouts and plenty of time. If you fail, you still need to force a three and out from your own 45 (34.5% chance of success) to have a chance. Even if they get nine yards in three downs the opponent has a choice between: 53yd FG attempt (highly unlikely); going for it on 4th and potentially giving Eli the ball at his own 36 with about 2 minutes left and no timeouts (maybe); or punt and try to pin the Giants deep (most likely). If you force more yards needed on 4th down, the odds of a conversion attempt obviously decrease and it becomes more likely they punt. The big advantage of option 2 is you get two chances to get the ball back and a 47.6% chance (statistical calculation) that at least one those chances will succeed.
The case for option 1 would probably be better field position if successful. Lets figure what expected field position would be. Last year the Giants allowed 23 yards per kickoff return so Dallas would likely get the ball at their 23 yard line (they actually got it at their 26 but we don't know that when deciding). Assuming the defense forces a punt, Giant opponents had a 42yd net punting average likely giving the Giants the ball at their own 35 to 26 depending on how many yards the defense gave up on the 3 & out. If you recover the onside kick, you get the ball at your own 45. If you fail to get the onside kick but force a punt, you will likely get the ball inside the twenty but there is a 28.5% chance of a touchback (NFL down inside the 20 to touchback ratio is 3.5 to 1). In the situation of an opponent punt, option 1 has an expected field position advantage of between 6 and 34 yards over option 2. Option 2 however, also gives the opportunity to recover an onside kick and be in a better position than either punt scenario. Given all these factors, I think it was a mistake for TC to forgo an extra chance at getting the ball back in favor of potentially better field position.