I actually love myrtle beach, it has been a second home to me, and they have been doing alot of work to clean up the town, like tearing down the pavillion. Not sure why you would want to go there for your senior trip though, alot better places out there. Not much for partying, compared to places like south beach.
We own a condo down there, so I can't give you any advice on renting a house, but I know that there is plenty to do there to keep you busy, but you may be disapointed with the nightlife, compared to large places like miami, or southbeach.
It's still pretty crazy though, and it will take you hours to cruise the strip on a friday night, and you will see plenty of boobies.
and if your going to party, don't stay in cherry grove, that is a old person/golf community.
If you do go, you should check out little river's gambling boats, you go out into international waters and gamble, cheap way of getting hammered if you know how to gamble properly