Just wanted to report back on my experience here as a data point. I was pleasantly surprised. Delta has really invested some money into these SkyClubs, and I hope they keep upping there game here as they really make going to the airport a lot more enjoyable. It's not quite as good as the Centurion lounges, but it's not too far off, and if I'm flying Delta, using these clubs are a no brainier due to how close they are to the gate of departure. I stopped by two SkyClubs at LGA:

LGA SkyClub by the Food Concourse in C Terminal:
-best SkyClub in LGA regarding the food offerings. For breakfast, they had all the offerings of the C28 club PLUS mini-cheese omelettes (which tasted better than I expected). For dinner, they had some solid offerings like a nice kale salad, Asian noodles, an edamame salad, and sesame chicken.
-they had an espresso machine (the SkyClub by C28 did not have one)

LGA SkyClub by C28 in C Terminal:
-Not as many food options as the main C Terminal SkyClub, but it seemed newer, and the decor and ambiance actually seemed a little nicer. They had big floor to ceiling windows and there was a really nice view to the planes taxing around.
-For breakfast they had two types of fresh fruit (grapes and pineapple), granola, yogurt, some basic pastries, two types of cereal, and hard boiled eggs. Starbucks coffee and harney and sons tea offerings.
-No espresso machine

Neither SkyClub was crowded at all. Also, there is apparently a third SkyClub in Terminal C when you take a right once you get past security. Didn't get a chance to check it out... maybe someone wants to chime in with their experience.

I have a Delta flight to Vegas out of JFK next month and I'm looking forward to trying out their flagship club at the T4 terminal!