Hyoyeon's surgery actually improved her looks (she had the weakest original visuals by far) a lot I'd say, but Sunny is one who looks bad in these videos with the surgery right now.
It's hard to tell what, if any, surgeries the others have had, because weight loss and make up can really make people look different. That being said I'd wager Taeyeon had a nose job. Yuri and Sooyoung have pretty much always looked the same since debut so I'd wager they have not had surgery, nothing major at least. Seohyun's face does look a bit different, but she lost a lot of weight when she switched to acting, so it's hard to tell.
But honestly aside from Sunny and Hyoyeon, who still look okay, I'd say the others are pretty hot. I'd take one of them any over some of these fat or tattooed chicks some people post. Beauty is in the eye of the beholder; to each his own.
Here's their debut stage from 15 years ago and I'd say they haven't changed that much for the most part. Keep in mind that they were wearing very light makeup and no eye makeup whatsoever so their eyes will seem smaller for sure: