Yes, no "guaranteed suite availability" for SPG - and even upgrade-in-advance SNAs are subject to availability and only 5 days out, and I believe Marriott removed the "suites excluded" terms - so both provide suite upgrades, based on availability, at check-in.

Marriott has better award redemption ratios (award nights earned per paid dollars/nights), using any realistic parameters I have analyzed. The tradeoff is that SPG provides award availability whenever rooms are available for sale (with very few exceptions) and MR still has limited award availability.

Marriott does have much better coverage - I current have 1 SPG property within 20 miles of my client site, but at least 6 Marriott properties. I have been in several locations where Marriott is my only option.

For the long haul - the lifetime programs are different but somewhat comparable (pending MR's changes to be announced). 10 yrs as PLT to get lifetime PLT is tough, but 500 vs. 1000 nights (800'ish if you factor in bonus nights and rollovers) is much easier.

I've been fortunate enough to be able to keep PLT in both for nearly 10 years and will be lifetime in both within the next year. If I had to choose one, I'd probably go with SPG, as the 25 stays/yr are much easier than 75 nights. Unless I knew I would do a lot of traveling outside of major cities - then MR becomes more attractive.