I have a pattern for teaching Sunday School classes now:
1.) Check out about 7 or 8 commentaries from the SPU library.
2.) Read/skim the first section of the most recent ones.
3.) Keep using the ones I find useful; don't use the ones I don't.
In this manner the 7 or 8 become 3 pretty fast, and that's usually more than enough information for each Sunday class. I taught a Gospel of John class from September to November this year and the winning commentaries were (in order in which I'd read them):
1.) N.T. Wright's John for Everyone (200something)
2.) G.K. Beale and D.A. Carson's Commentary on the New Testament Use of the Old Testament (2007)
3.) Craig S. Keener's The Gospel of John: A Commentary (2003)
4.) D.A. Carsons's The Gospel According to John (1990)
With the exception being that often Keener would quote Carson and put him into context, so often I could stop with Keener, while agreeing with much of Carson's work.
I especially want to point out how great Keener's work was. Its deliberate focus was on the social and historical context of the Gospel of John, which means he would talk about how that language or official position or whatever was used in Greek and Roman contexts, as well as Second-Temple Jewish contexts, and even the post-biblical Rabbinic literature. For the historical perspective alone this was far and away the most comprehensive, and Keener had welcome pastoral and theological insights as well. I am thinking I may move on to the Gospel of Matthew just because Keener has written a commentary for that too!