I would think the fighting around the pacific Islands differs somewhat from that In Northern Europe. YES the Marine Corps were good, but at that stage they were also very specialised and you can bet your bottom dollar that in a straight out and out fight the Marines would have one hell of a job ejecting the likes of LAS from a town or city in europe, just as LAS would be slaughtered trying to fight in the pacific theatre against the American forces there.
The comparison of fanatics doesn't hold so true either. LAS and other combat units of the SS were not quite as fanatical as their Japanese counterparts, this is more myth than reality. Their tendency for higher casualty rates mostly comes from the commanders of their corps/armies throwing them into the hottest part of the front and handing them the worst possible jobs, hence their higher rates, but more often than not they got said job done. They weren't all maniacs though, many of the SS formations were well trained, well lead, well oiled divisions who knew full well the best tactics of their time and operated under them. They had no more tendency towards fighting to the last man than any other elite formation with the exception of the end of the war naturally when many had nothing to loose.
As for marines KO'ing the tanks, well again this depends on the situation and formations involved, firstly the SS were not the morons depicted in Saving Private Ryan. Units like Hohestaufen and Frundesburg more than proved their capability for street fighting, and destroying dug in formations, you only have to look at the Arhem campaign for that, when they had barely 1/3 of their forces and 1/10th of their armour to begin with and were suprised by two of the highest quality formations the Allies had in the entire Theatre. Hohestaufen reacted well and cut the threat off before they proved their mettle, gradually forcing the Paras out using well tried tactics. Also assuming it was a relatively intact SS formation they would have excellent supporting arms such as heavy artillery and well mechanised infantry, giving them the edge in both manouverability and firepower on the ground.
The marines on the other hand would have little or no experience of fighting that type of formation, and especially little experience of engaging a heavily mechanised formation such as LAS or the like. This wasn't what they were trained, equipped or designed for, and frankly I would suggest that unless they could adapt mid battle they would simply be mauled by a fast moving, hard hitting bunch of combat vetrans who'd already cut their teeth years before fighting elite formations and beating the living daylights out of them all too frequently. Not that this makes the Corps non-elite, they were, BUT they were then and by and large are now specifically for certain types of mission as previously stated, and fighting elite Panzer divisions on a theatre they had no experience of simply wasn't it. A hard fight it would be, but I would be confident that the vetrans of the SS would come out on top in the end
Ultimately the SS were used to engaging elite formations similar to the marines and more often than not trouncing them. The Marines never had the chance to experience what engaging such a formation would be like, and whilst they would do well, their inexperience would hamstring their battle. (I don't buy for a moment a comparison between the Japanese army and the Waffen SS)
Which btw is the point on efficiency, ie the corps are arguably the finest formation for their numbers anywhere in the world, then or now, but they are not the be all and end all of the US military. I tend to prefer to look at the entire military (or in this case the army of a nation) and determine their worth from this overall picture. The Corps to a degree needs the army for the more mundane roles as mentioned. Also not all people in armies can meet the standard set by certain elite formations within it, that is why marines, SAS, paras and such like exist. Simply saying all should conform to the standard made by those formations won't work, because by and large the bulk of an army never can and never will match such a standard, it's simply not possible.
I have immense respect for the Marine corps, but when considering the most efficent army, they don't get their own mention. No more than the Waffen SS can be seperated from the Wermacht, or the Panzer formations from the infantry, or the commandos from the British army, the Marine Corps are for me considered as part of the ability of the overall US army. They're an elite branch of a decently efficient army, but alone they simply won't be enough and should not be considered seperately.
Because concentrating on a specific part of any nations army it's possible to show how such a formation was specifically as good or even better than the marines in their time as long as you're selective enough....