I fly to NYC every month and take the Delta non-stop flights between MSY to LGA round trip. DL began using NWA metal for these flights a few months ago which means that you will be on a Airbus instead of a commuter.
Oct 15: DL4124 LGA/MSY non-stop departs LGA @ 9:55 am
Oct 20: DL4134 MSY/LGA non-stop departs MSY @ 7:35 am
I usually book the cheapest fares available when I book and almost always get upgraded. In fact a few weeks ago I sat across the aisle from Nicholas Cage on the morning flight out of MSY!