Agree with the comments above, but I would be more likely to say "sofa" to describe a small couch or loveseat. I almost never say sofa though - normally couch. When I lived in the UK I seem to remember people saying "sofa" more often but I will defer to someone from there to confirm.

they're the same. :v

Both are fine, actually. Either words are okay to use in any situation~ "Oh! I love your couch!" "Your sofa is so comfortable." "Your cat is sleeping on the couch again..." "I want to buy that sofa, but it's so expensive."

In my experience, they mean the same thing but depending on where you're from, you've usually been raised to say one or the other. Myself, I never say sofa, I only say couch. I have friends who have been raised with the word sofa, so they only say that. Hope this helps :)