it was common for Germans to prefer fighting Americans versus other Allied nations.

While this is true, it's commonly noted by many historical accounts that this was an inaccurate perception derived from poor performance early in the war. A lot of the accounts I've read cite the adaptability of the American forces as nothing short of exceptional. In particular, the aftermath of Kasserine Pass saw sweeping reforms of organization, tactics, and strategy, in some cases in as short a time as a few weeks. Several of the histories I've read suggest that constant Axis underestimation of American forces, particularly blooded formations, was actually to the benefit of American forces. Even Rommel consistently underestimated the American forces (despite the rapid improvement they displayed in the Africa campaign).

The difference between blooded and unblooded formations is absolutely astonishing, as well. Veteren American formations were easily the match of any unit in the theater (particularly the 1st Infantry Division, the Airborne divisions, and the Ranger battalions, at least from my readings), but some of the untested units were undertrained and unprepared, in some cases receiving advice on combat from their Wehrmacht prisoners!

At the end of the day, though, the chance of survival and eventual return to the homeland was empirically higher when surrendering to the Western Allies than the Soviets, for a variety of reasons (for example, when the Sixth Army surrendered at Stalingrad, the Soviets had insufficient food, supplies, and medical attention available for their captives). That alone may have contributed to the preference for fighting Americans. Certainly, by the time of the Normandy landings, at a leadership level, fighting the Americans would have been nightmarish, given their utterly overwhelming air superiority, nullifying the armored columns that the Wehrmacht used to such advantage earlier in the war.

EDIT: It is worth noting that the American forces had, in many cases, inferior equipment. The MG42 was dramatically superior to the .30 caliber machine gun the Americans deployed. Americans were piloting Stuarts into war against Panzer Mark IVs in Africa and Shermans against Panthers and Tigers in Normandy (which sported the feared 88mm gun, possibly the best gun of the war), both of which were matchups in which the Americans were dramatically outgunned. Shermans also ran on gasoline and had poorly protected magazines, which made them notorious firetraps (the Germans called them "Tommycookers," and the British nicknamed it after a brand of lighter noted for consistent ignition). By the end of the war, the German forces were fielding the MP44 as well, meaning that the Allies were facing the first assault rifle down with semi-automatic and bolt-action rifles. In that regard the common perception was wholly correct; the American forces had an overwhelming preponderance of materiel, but for the most part it was technologically inferior to the German equivalent.