I fly out of LGA extensively and I have never had to wait to get into the club, nor seen a line. I generally take 8-9AM flights so I might miss the early morning rush. This is in comparison to JFK T4 which sees consistent long double (e.g. D1/DM, and everyone else) lines from like 3PM on nearly every time I fly out of there. JFK has been a nightmare ever since they closed T2 and moved everything over. I usually go to the Amex lounge now for quick food before a transcon flight. Its an awkward lounge, but usually no line and decent food.

As many have said in many threads, the LGA sky club opens at 5AM, so there is usually a line before that time of people waiting to get in.

ORD is the nicest club. The amenities and food are top tier, the staff are amazing, it is never that busy, and flights to LGA boards from the connected gates which bypass like the entire boarding queue. LAX and SLC come in a close second, but they get very busy and are filled with obnoxious people from California.