pinniped

Yea, this was never a common theme on the SPG board. Minor quibbles with the app or needing to call for certain things, but I can't recall any widespread problems with booking, points posting, redeeming, status showing up, etc. Seemed stable to me. If they ever had a catastrophic outage, it didn't know about it: it would have happened at a time when I wasn't trying to book or complete a stay.

Marriott was reasonably stable too. It's just the merger process itself that has been a dumpster fire.

Hyatt has had serious, widespread IT problems over the years, including at least one catastrophic (many hours) outage that I'm aware of. Fundamental issues where you could not book a regular hotel stay at all - not just some sort of Gold Passport issue. Hilton has had some wonky UX in the past, as they never seemed certain whether they wanted members to use HHonors.com or individual hotel brand sites. (Multi-login problems, data not being saved, etc.) These problems seem to have been mostly resolved in the past year or two though.