My first reaction is to keep the coat. It sounds like a more practical item. As the mom to littles I've learned that things I'm not comfortable wearing around them, rarely get worn.

Can't wait to see the showdown!
Let's say they were equally gorgeous on you.
The coat is outdoor-gorgeous, but goes on the chair back or coat rack indoors. But, still fab striding about town on errands and such, or "arriving" somewhere.
The blazer is outdoor-mild and indoor a lot, out with DH, nighttime out with friends (yes, that will happen even with toddler!).
Or sometimes, I'll have a situation where I decide neither is right, and I need to look for _____ ! Put that in your bonnet!