The argument can certainly be made for Scranton's Charlie Winston. Season 10's NL Fireman of the Year is Camp's all-time leader in saves with 287 (leads second place Ricky Adkinson of Tampa Bay by 92 saves) and with another average season this year, he'll become Camp's all-time ERA leader (needs just under 80 IP to qualify).
The 8-time All-Star has made every All-Star team since season 2 and is also a 3-time Fireman of the Year (two times in the AL, once in the NL).
At 32-years-old, Winston enters season 11 (his fourth in Scranton) coming off one of the best seasons of his career. Last year he saved a career-high 37 games in 41 opportunities while pitching in a career high 82.2 innings and posting a 2.18 ERA. Winston also enters season 11 in the final year of the 3-year $17.4 million contract he signed before season 9. The last two seasons in which Winston was expected to be a free agent the following season were the best two seasons of his career (seasons 3 and 8).
And with Ricky Adkinson's reduced save opportunities in recent seasons, Winston has a chance to record 300 career saves before any other reliever can notch 200. Best closer ever? I'd say so. And he's not done yet.