I don't know why all the hate for LGA from Delta fliers. Both C and D are rather nice, as airline terminals go (though D is not terribly aesthetically pleasing, and C is still a little rough around the edges in places, because of the renovations).
Since taking over C, neither C nor D are outrageously crowded, like D used to be, and there are plenty of amenities. The new long bar thing in C is pretty cool too.