It depends on what BITOG members who have used both in the same vehicle say. I see no other way to compare them to one another.
I use Mobil-1 in one vehicle - Pennzoil Platinum in another. I'm not about to change until either vehicle starts consuming either oil. So far - after two OCIs, the dipstick remains at the full mark using either one.
So if it ain't broke - I ain't switchin' brands or weights to do a comparison test..
I've used Mobil1 in my '00 Grand Am for 85K miles. The engine is spotless on the inside and runs great. I'd definitely reccommend Mobil1.
However, PP looks to be very good. I've stocked up here recently. The PP will be going in my '05 Mazda3. I've heard a lot of good things about PP so I'm going to give it a shot. Especially, with it being cheaper than Mobil1.
Sicky topic, buy whichever one you want! if you always do what other people say then you can't think for yourself...
but if it were me I would use whichever brand was on sale the day of the oil change.