Spirit, Frontier, American, United, Delta, JetBlue; i'm sure I'm forgetting a couple. The only airlines that are exclusively Boeing are Alaska Airlines and Southwest.

Alaska isn’t exclusively Boeing ever since they bought out Virgin America and its A320 fleet.

Most legacy carriers globally have ended up with some of both Boeing and Airbus.

Just anecdotally (and I expect this doesn't hold statistically), I don't even notice a difference in manufacturer distribution between these US and EU airlines.

I believed I've flown Delta Airbus planes, but they have Boeing planes too.