Most of our loan players who have done well we have ended up signing. Kightly, Jimenez, Helder Costa, Jota, Jonny, Boly, Dendoncker, Cunha... even ones with just a decent contribution like Ait-Nouri, Guedioura, Hwang - all signed. If we didn't sign O'Hara then his loan spell and what he brought would be a massive positive. Doumbia was really good at first. So was Bonatini!
If we're only talking players that didn't sign permanently: Alfred N'Diaye was good, pleasantly surprising too as he was underwhelming going off his previous appearances in England. I thought Peszko was decent. When I was a kid I liked Frimpong. Vitinha is the one who got away but surely can't be anyone's favourite loan player. Even if there was clear potential, Nuno didn't use him.