I agree with Sab (
pgc hunter) that summer (I'd include early autumn too) seems to offer more nights with decent seeing than winter/spring. Many of the nights offering the best seeing seem to be still, warm and slightly hazy (lousy transparency but good seeing). The nights offering the best transparency are often the opposite, e.g., shortly after big cold/rain fronts pass through you sometimes get great transparency but the stars are twinkling madly.
Even on nights of poor seeing there are usually small periods when the seeing momentarily improves and more details can be glimpsed. Also, larger apertures collect more light which improves the colour saturation of the image making some features easier to distinguish.