HogansHero said: "I would definitely not take a bus (or taxi, Uber, minibus, etc) from EWR (ever on Sunday at that hour but especially with the double whammy described above). I would also definitely not take anything other than the subway into the city from LGA (with the bus connector). As I said above, an hour either way, and no one can predict flight delays. (Also check the weekender schedule on subway changes.)"
Since it's a morning flight, delays are less likely. However, Southwest is only slightly better than Spirit when it comes to delays, so that's a wash as to which airline will be more reliable. As Hogan said above, excepting for any flight delay (or luggage problems), either lands in time to catch a matinee performance.