There is absolutely no difference that I am aware of. And in my region of the USA we use both words- whichever comes to mind quicker.

Whichever I choose to say is a matter of which one I feel like saying. The same piece of furniture could be called a couch or a sofa. I don't think there is any difference at all in meaning.

I use "sofa" more often because it is easier for non-native speakers to understand. I just googled it and here is the answer that I found. "Both terms can be used interchangeably; however, in former times, a couch was a low, bed-like piece of furniture for lying on. A sofa is more benchlike with full arms and back."

お早うございます、Kojiさん It's an interesting question. They mean the same thing, but have different origins. You can check on this link: https://www.google.co.id/amp/s/www.elledecor.com/design-decorate/amp9154/couch-vs-sofa/. すばらし一日を。 玲玲