I stayed at the Marriott a couple of months ago and had a mixed experience as a SPG Plat who matched into Marriott Plat but had 0 stays at Marriott prior to the Pittsburgh stay.

Long story short. Hotel is in great shape. No upgrade as a Plat - actually downgraded-ish (given room with two doubles instead of booked king - but since I was staying alone and only for one night I didn't push). Burger bar in the lobby was very good and reasonably priced. Staff in Bar and Lounge was amazing! Room was very clean.

Best part, lounge was amazing. Always staffed at meal time. Multiple hot dishes during breakfast and dinner. Drinks 24 hours. Honor bar during food hours

I'd stay at the Marriott if you're there for an event at PPG unless you really have to have SPG credit.