I'm well aware the vast majority of German soldiers were on the Eastern Front but I'm a little confused about the quality of those the Western Allies faced. I've heard and read on the internet (mostly message boards or comment sections) that the German soldiers on the Western Front that American, British, and Canadian forces fought weren't as well trained or equipped as the soldiers on the Eastern Front. One comment even suggested they were "old men, kids, and the infirm with smatterings of SS here and there" which I'm assuming is hyperbole. Also, how much of a role did the Waffen SS play on the Western Front?
I'm going to to preface my answer by saying that it may not be everything you're looking for since I'm only a student who's about to start grad school but I'll give it a go because I hate seeing questions going unanswered.
One of the major factors that you have to take into account when talking about the quality of troops the Allies faced on the Western Front is how late Operation Overlord occurred in relation to the timeline of the war. By June 1944 the Germans were only 10 months from defeat and as time went on the Wehrmacht just could not replace what they had lost both in manpower and supplies. This meant that as time went on, the quality of opposition the Allies faced gradually decreased and indeed you would find kids as young as 16 fighting for the Wehrmacht. There is a common saying that the Soviets took the brunt of the German war machine and this is largely true. The battles of Stalingrad and Kursk in 1943 served as major turning points in the war and cost the Germans a total of around a million men. The men lost in these battles were also some of the most experienced soldiers in the Wehrmacht, many having seen action during the invasion of Poland in 1939. Hitler had diverted many of the divisions lost in these battles from the Western Front before the Allied invasion, believing that the Atlantic Wall would be enough to stall a potential invasion. After the Germans lost in Stalingrad and Kursk, they were unable to replenish their numbers and were put on the defensive for the rest of the war. Unrestricted Allied bombing of German cities also meant that the ability of Germany to produce goods for war was all but extinguished by the wars end. The Germans even went as far as to try to build factories in caves and mountainsides in an attempt to protect them from bombing.
From October 1944 to the end of the war, Goebbels was in charge of the Volkssturm (people's storm), a "volunteer" force consisting of German civilians aged 16-60 who were often pressed into service by the SS under threat of execution. This is where the image of old men, kids, and the infirm comes from, and images of the Volkssturm defending a ruined Berlin are still some of the lasting images of the war.
As for what role the Waffen-SS played on the Western Front, the Panzer divisions of the Waffen-SS were present during the initial Allied invasion and tried to make their way toward Normandy but were largely cut off by paratroopers before they could reinforce their comrades on the beaches. The story of the Waffen-SS is similar to that of the Wehrmacht. During the final months of the war, due to lack of supplies and a growing inability to adequately replenish manpower, the Waffen-SS by the end of the war were all but finished. Sepp Dietrich, one of the highest ranking members of the SS and who was put in command of the 6th SS Panzer Army remarked,"We call ourselves the "6th Panzer Army", because we've only got 6 Panzers left" in the final months of the war.
I hope this answers your questions! If you're interested in German tactics during the war, I suggest picking up "Blitzkrieg, From the Rise of Hitler to the Fall of Dunkirk" by Len Deighton.
Edits: Added some info and fixed my typos