I voted for plain mono, but I do love the mon mono. My personal reason for not getting a mon mono? If/when I get married & my last name changes, I want the bag to match! It's funny, I have tons of things heat-stamped with my current last initial, but I think the prospect of paying that much more for a mon mono is what keeps me waiting til I tie the knot! (What will happen to my heat-stamped bags, you wonder? I'll deem them "vintage" haha!)
But if you're a normal person and not worried about silly things like me...then go for the mon mono! Personally I'd be worried the personalization would come off with time/heavy use, and feel the plain would go with way more things.