I have taken a lot of 1000+ mile CR9s. Most frequently RDU-AUS and winter schedule ORD-SLC. On the former, F is often just $99 more than Y. Easy choice unless you are Diamond.
In the 500-800 mile range, ORD sees a lot of CR9/E75/E70. ORD-LGA is mostly E75, ORD-JFK has been all CR9 for as long as I can remember.
In F the CR9 are fine in an A or C seat, a little difficult from a D window. But generally easy upgrades.