They have virtually identical approvals (SN, GF-5, Honda HTO-06, ACEA A1/B1 & A5/B5, dexos1). The M1 EP has a slightly higher flash point and the PP has a slightly lower pour point, but all their FP and PP temps are excellent. The viscosity index is virtually identical between them (169 & 170).
The M1 EP line is specifically marketed as a 15,000 mile long life oil, if that is an important consideration for your application. That's not to say the PP couldn't also do an extended drain - we see good results from both in UOA data frequently.
Sorry if this isn't much help. They are both very similar, excellent products. Pick the brand you like best, or the one that's on sale.