Longstreet or Jackson?

This morning on ESPN’s First and Ten Jay Crawford, Skip Bayliss, and Rob Parker debated which Yankee, Derek Jeter or Mariano Rivera, was more essential to the Yankees’ success over the last sixteen years (as much as I think highly of Jeter, I think Rivera’s virtually irreplaceable).  We do the same thing when it comes to Civil War generals, and so I ask: as part of the Army of Northern Virginia, who was more essential to the success of that army: Thomas J. Jackson or James Longstreet?

Note the important qualifier: as a part of that army.  Yes, Jackson’s Valley Campaign of 1862 receives its plaudits, and one can say that indirectly it helped the Army of Northern Virginia stave off what might have been disaster in the spring of 1862, but I’m not asking who was the better general (and by framing the question in this fashion, I also avoid discussions of Longstreet’s own adventures in Georgia and Tennessee).  However, between Lee’s right arm and his old war horse, which one was more indispensable to the success of that army?  Which one could Lee less afford to lose? 

Yes, he lost Jackson, but what if Jackson had survived Chancellorsville and Longstreet not made it back to join Lee?  Would we be asking  “what if Longstreet had been at Gettysburg?” Surely Lee missed Longstreet during the Overland Campaign.

The comments section awaits.