I'm in a keeper league and can get Ovechkin for Hartnell and St.louis. As good as Hartnell has been I don't think his value will ever be this high again. St.Louis is a solid keeper but he's old. Seems like a no brainer right?
Personally I would try to get more than just Ovy while Hartnell's value is so high and St. Louis is playing well. And just dont forget, St. Louis has been "old" for a while, and doesnt really show any signs of slowing down. As long as he plays next to Stamkos, I can see him holding value for the forseeable future.