All things considered, for me probably Buffon. Iker was gifted, produced many special moments and played behind a shit backline for a decade, but you always had the feeling he wasn't really a 'worker' and was hardly ever scrutinised for his imperfections, because of how good he could be on a good day and how shit Spain were in his formative years. He had this Spanish umbrella of protection over him all along after he displaced Canizares in early 2000s. I loved the urgency and the passion, but the inherent limits got more and more obvious towards the end of his career. Many people remarked how he didn't really have to train exceedingly hard to remain at the level he and the coaches thought was sufficient. Gigi for me always had a lot more polish and longevity, even if that CL final at 38 was rather poor. But they're very different as keepers. If I had to take one for a pickup game, I'd take prime Gigi. But I love Iker and would never change him for a different keeper given the opportunity.
Incidentally, Navas will always remain the underrated keeper of the lot and is an excellent comparison when talking about Casillas. I always thought he would have been as legendary as Iker, if not more, had he come through Real ranks at the same time. The way he peaked solely based on work ethic was extraordinary, almost unprecedented, particularly for a guy with not really strong early career background. He has many of the same limitations and is slightly more error prone, but if he hadn't succeeded Iker, he'd absolutely be a club legend at the same level. To me he is as important to the serial RM success of 2015-2018 as Casillas was to the several campaigns in the noughties.
