I've had nothing but good experience with IB, though their FF program is so bad it's a joke.

Vueling, the new Spanish LCC, is partly owned by JetBlue, flying similarly-configured new A320s, and my one experience with them (flying Barcelona to Seville) was perfectly pleasant and efficient. Did I mention the flight cost 10€ each way?

A few weeks ago I was on a UX flight BCN-MXP and back. These guys have really gone downhill. Granted it was an hour flight, but the ENTIRE time they were on the PA hawking cans of soda, "duty free items" and 10€ sandwiches. I got to the airport early and wound up waiting for two hours before their sole agent showed so I could go find a lounge while I waited.