If you don't have a gear boat the South Fork American is a great option because you can run it as two one day trips and therefore don't need a frame or anything.
If they want the "wilderness" experience try the Middle Fork American. It's low class IV and offers good scenery and hiking. You will need a multi day set up and there is a portage on day two that's a bit of a pain.
As for gear rentals, it's a bit of a pain out there. There are a few places, but none of them are amazing in my experience.