I went receptacle for ease of transport/removal of panel. In my first control panel it was attached, and having to lug that big thick cord around attached to the panel was a pain for me; unwieldy, would knock things over, more difficult to store the panel away, etc. That is why I do not have mine permanently attached any longer (and I got my twist locks for $18 for the male/female).
That's what I did but I'm using a very small Auberins enclosure. I just put two 12" pigtails on the back with two twist lock connectors, one for the power cord and one for the heater. I didn't even opt for the fancy strain reliefs, I just used the EMT ones that have two screws for the clamp.