If I'm being honest, I tend to ignore older commentaries. In the back of my head it seems like I've tagged them as being outdated, not up to speed. Instead, I jump to the latest or most respected. If my question hasn't been dealt with, then I'll start making my way "to the bottom of the list". And so this is how I ended up consulting Matthew Henry’s commentary yesterday: I stooped to the bottom of my totem-pole of sources since none of the more modern ones had explained (adequately, in my opinion) what type of covenant Jonathan and David had “cut” together. Yes, of course, label it a “covenant of friendship” but what does this mean? What are the stipulations? What oaths are taken? These are all topics that lie silent beneath the text.
This is where my newly appreciated Mr. Henry stepped in.
[…] they seemed but as one soul in two bodies. None had so much reason to dislike David as Jonathan had, because he was to put him by the crown, yet none regards him more. […] He endeavored to perpetuate this friendship. So entirely satisfied were they in each other, even at the first interview, that they made a covenant with each other, v. 3. Their mutual affection was sincere; and he that bears an honest mind startles not at assurances. True love desires to be constant. (Matthew Henry's Commentary on the Whole Bible: Completed and Unabridged in One Volume, Logos version).
Now I’ve always believed Lewis’ sage words concerning chronological snobbery, but Mr. Henry simply (and strongly) reminded me of their truth in his heart-felt exposition. (O yeah, and thank you Logos for giving me resources that I thought were fluff, but have proven otherwise).
 An exception is Keil and Delitzsch’s Commentary on the Old Testament. I am always impressed by the way they engage the original languages in addition to the more typical model exegesis that is common to commentaries.