I think the culture at both places is great. I interviewed at both and, like you, got CJOs at both, ultimately deciding on Republic.

I'd echo what others are saying; if you want LGA, YX is a no-brainer. You likely will hold a line by the time you get done with IOE. Even if you are on reserve, you'll fly 40-50 hours a month at a large domicile like LGA.