I use TDAmeritrade, and by placing, changing, cancelling replacing etc I see that they use a number of different MMs for the same security.
Companies like SpeedTrader used to (not sure if they're even around anymore) let you choose the MM that routed your order, but for the rest, unless you have Level 2 there's no way to tell that I'm aware of.
Your life is trite and jaded,
Boring and confiscated.
If that's your best, your best won't do.