These oils have very similar add packs and similar basestocks.
SOPUS tells you right up front that they use Grp III, while XOM dances around and tells you they use a blend of basestocks in different grades.
Rest assured that M1 5W-30 uses Grp III, and I state this as informed opinion.
PP usually has prettier UOAs than does M1, for what that's worth.
We have at least one member here who's done 10K OCIs on M1 since dirt was a new thing, never done a UOA and has had good results over long mileages.
Flip a coin and take your pick.
I've used entire stash's worth of both over the past thirty years, although PP has only existed for the past seven years or so.
IOW, I've used a lot more PP since '05 than I have M1, and I have very pretty UOAs for my two oldest Japanese cars to show for it.
If M1 were as heavily promoted with MIRs as PP has been, I'd probably have used more M1.