For the two 5e games I run I'm nowhere near needing to consider this question.
5e Game #1:
Runs every week
*Is ambling towards a trip through Barovia,
*then probably Avernus (re-written for considerably higher lvs.)
*But 1st they'll get one of the chapters out of SKT (seems a waste to have only used the Hill Giant section). Sure, different characters actually completed the adventure in a previous campaign, but the Stone/Frost/Fire/Cloud giants were up to their own agendas off-screen during that. Plenty of space to tell the tale of a different party dealing with some of that.
This is enough content to last 2+ years. And then you have to consider that these players will cheerfully hare off on adventures of their own choosing.
5e Game #2:
Runs every other week
*Right now they're gaining early lvs via the short adventures in Dragon of Ice Spire Peak from the essential kit.
*Next up I envision running one of the chapters out of SKT. Most of the players in this game were the ones who played that adventure the 1st time, going the Hill Giant route. So current characters vs the Stone/Frost/Fire/Cloud plot (chosen from one I don't use for Game #1) they didn't get to see the 1st time through.
*Eventually a trip to Avernus (again, re-written for higher lvs)
For this group that's enough material for the next of never....
** I basically inherited Game #2. Their DM had to drop due to work schedule, & while I don't mind filling in, I'd also like to only DM 1 game, preferably on Thur.... So I'm hoping that I can merge these two games.
Pathfinder:
Played with 100% different people than the 5e games. Right now we're about 6 months away from completing the current AP (assuming no TPK). Right now I'm on the player side of the screen.
But we rotate GMs each campaign. How our pattern seems to work is: Me, player A, Me, Player B, Me, Player C..... So I almost always have to have an idea on tap as I'll either need it either 6 months out or maybe next week.
Currently I'm thinking of running a PF version of ToA. Since I ran this last year for the 5e games all the maps are printed, all the minis collected, most of the basic prep is done. So pull out the PF Bestiary, plug in some #s, & Welcome to the Jungle.