Frankly, if pure speed of reloading was the crucial factor, I'd want a Mannlicher bloc clip action. Probably one of the reasons those marines grabbed those 88s. (The Lee Stripper clip is a PIA. Y'know, I've stripped off so many thousands of rounds of 5.56 into M-4 magazines, and no 2 of those clips acted the same. Same with Mauser and Lee Enfield clips. At least with the Mosins the interrupter meant I didn't have to worry about stacking the rims)
If you know your SYSTEM (Krag, Mannlicher, Mauser, etc) and are willing to work with it, they're all good. I like Krags myself. As for the Marines and the Krag, I suspect, like so many things, it just depends on who you ask. (or whose letter you read) Certainly they liked it better than the Lee. Though the Lee, like the 03, has drifted into the haze of Legend . . .
I can load a Krag pretty fast. But when it comes to shooting one, I bow to the Legend of Sgt Isaac.