The MM sounds like a better fit if you're including a handbag, lunch, plus some essentials. You'll have a little room left for incidentals like a light sweater, scarf, etc. The PM will fill up quickly.
I've heard the PM described on this forum as a purse where the MM is a tote. I thought that description was apt.
I've heard the PM described on this forum as a purse where the MM is a tote. I thought that description was apt.