atm the best one is handanovic for me. (not meaning to be a hipster, I do rate him that high)
that doesn't make u a hipster, it just emphasizes the fact that u follow serie a closely. if there were more serie a followers in here, u'd probably see a long list of posts with one name alone (and that name would be handanovic).
buffon is not the Godly goalkeeper he was until 2 years ago. there has been a dip in his performances (probably due to injuries and aging), wich led him to commit a few blunders every now and then. having said that, i'm pretty sure his blunders over the last 3 seasons were still far less than neuer's blunders (and i'm picking neuer, as he's undenyably a top class keeper today).
practical example; let's imagine a 33 years old messi would miss 30% of the scoring chances he produces today. 30% is a pretty big number and would certainly make messi far less "good" than he is today..... but it would still leave him among the very best scorers on the planet.
buffon has been for over a decade on a ridiculous ("messi-esque") performance standard, wich made him simply uncomparable to pretty much any other goalkeeper (the only one who got close to him was casillas). today instead he is "just" a top class keeper, wich means that, over a short span, his average performances might be worse than some other top class keepers. for instance (in my opinion) over the last 2 seasons, handanovic has been a better keeper than buffon.
as for the other names i read in here, i'm not so sure. casillas isn't even playing at the moment, so it's hard to tell. Lloris, begovic, cech, caballero, and valdes are great keepers, but saying they're on the same level of buffon, handanovic and neuer is a bit of a stretch imo.
as for de gea, sirigu, mignolet and curtois, they're all very promising young keepers and in my opinion comparing them to the likes of buffon, handanovic and neuer would be just wrong (and also unfair, as they still have margin for improvement). also i should mention that i haven't been able to follow sirigu closely since he left palermo, so i couldn't even really tell how good he is right now
nowadays i don't watch as much football as i used to, but i get the feeling that, whereas the average level of goalkeepers raised substantially (there seem to be far more good keepers today than 10, 15 years ago, especially outside of italy), the top class standard dropped a little bit..... meaning we have some top class keepers today, but they wouldn't stack up well against "past top class keepers", such as buffon, peruzzi, toldo casillas, schmeichel or pagliuca, for instance.