As someone born in the 90s, I've only heard the term "erector set" maybe 2-3 times ever (I feel like maybe I remember it mentioned in a Calvin and Hobbes comic, or something of that nature), so I have no knowledge about which term was more common, but one of them kind of sounds risque to me...did the word "erect" not have that connotation back then? It's not hard for me to imagine kids (or even adults, really) giggling every time someone used the term "erector set", so I'd expect that to be something people remembered more than "Meccano", which to me sounds like the name of a coffee brand or something.