The reason I prefer the larger expansions or modules is that as said, they tend to be more universal and reasonably easy to figure out.
Purely hypothetical and just to illustrate the point, can you imagine trying to organize a game with someone and you said "oh I have the base game, DLC 1, 3, 7, 9 and modules 3 and 1" and your opponent said "I have base game, DLC 1, 2, 5 and 6 and only module 3". I remember considering buying the Bad Company 2 Vietnam expansion as it looked like a good chunk of content at only $15, that was until I played it on a friend's computer and found out how difficult it was to find populated servers, and even they dropped off fairly rapidly after launch it seemed.
Choosing a mission without resorting to "lets only play base" would be more tactically challenging than any mission you could pick