Well I agree that any victory achieved without blood and in this case the annexation of Austria and the Sudetenland was impressive but I think the original question was during World War II.
The victory at Kiev in 1941 was impressive but we tend to forget that the Germans lost was also huge: 100 000 dead and casualties. The victory in Western Europe in 1940 was not complete since they didn't defeat England so I would have to say that the defeat of Yugoslavia in April 1941 was Germany best victory, there was absolutely no failure by the Germans in that operation. Here is an excellent article about that Battle on this site:
We've already been through this, haven't we?
If we understand the Kiev battle as the German envelopment operation: The overall German combat losses in September were just above 140,000. If one adds up the reported losses of the army commands between 6 September and 6 October, you get an essentially similar figure. More than 40,000 of these were incurred by HG Nord (including PzGr 4). HG Mitte suffered a little above 45,000, while HG S lost almost 50,000.
Of course, some of the formations of HG Mitte took part in the Kiev battle, while some of HG S did not, depending on how you define the scope. Timewise, the period used here is a little bit on the long side. If you define the force scope as AOK 2, AOK 6, AOK 17 and Pzgruppen 1 and 2, the German losses come to ~45,000. Most of the AOKs who lost most heavily did not fight at Kiev; AOK 11, 6, 4, 9, 16 and 18 all lost between 15 and 20,000 men during this month.
If we apply the same "long" definition as used by Krivosheev for the Kiev defensive operation, which includes basically all fighting in the Ukraine except on the southernmost sector between 7 July and late September, then we must add the July and August losses (or to be precise, losses between 6 July and 6 September) of AOK 6, AOK 17 and PzGr 1, which come to roughly 100,000.
In other words, if we define the battle as encompassing the German envelopment operation, 100,000 is a much too high figure. If we define it, as Krivosheev, as encompassing basically the whole major battle in the south for a period of more than two and a half months, it is much too low.
In simple terms - if you define "Kiev" so broadly that it is basically synonymous with the summer campaign in the Ukraine minus the border battles, you get a big figure. If you define it narrowly, as the September envelopment operation, you get a small figure. Either way, in the context of the war in the East at the time, there's nothing special about them - it's basically what you would expect anywhere in the East for a force that size for that such a period of time. That also goes for the overall relation between the German and Soviet losses (by the long definition), which is roughly the same as for the year in general. Of course, this is also an argument against the Kiev battle being any special German achievement. But this would look different by the short definition, since a much larger part of the Soviet losses took place in September.