There really wasn't a good analogue for the B-17 in the Luftwaffe.

The Luftwaffe's bomber force was designed around two main concepts - the interwar concept of the "fast bomber," and dive bombing. The Luftwaffe was largely tactical in focus, a consequence of the heavy lobbying of dive-bombing advocates like Ernst Udet and the unfortunate death of Walther Wever, the prime advocate for strategic bombers. During the interwar period, General Wever headed the Ural Bomber program, which led to the development of the Do 19 and Ju 89, both of which were four-engined strategic bombers intended to have the range and payload to strike strategic targets beyond the Ural mountains. However, Wever died in a plane crash in 1936, and the Dive Bombing clique in the Luftwaffe took over, pushing their theories.

Prior to this, though, German bombers were developed as "high speed mail planes" along the doctrine of fast bombers. The results of these efforts - the Do 17 and He 111 - were both designed around the reality that, given the early warning systems of the time and capabilities of contemporary fighters, it was possible to design bombers that were, for all intents and purposes, next to impossible to intercept. The result was a focus on speed over protection, with early concepts for the Do 17 lacking any protection at all. Unfortunately, the "Fast Bomber" concept was overtaken by fighter performance in a manner of a few years, and they would all eventually be given defensive armament.

The Ju 88 was originally designed to this concept as well, but it was overtaken by the Dive Bombing craze and would be strengthened to allow for dive bombing at the cost of raw speed. While the Ju 88 would end up being Germany's most capable bomber at the outbreak of war, it was still very much a medium bomber, albeit a very versatile one.

The closest thing Germany would have to a "true" strategic bomber during WW2 was the Heinkel 177. It was conceived in 1936 to meet more demanding "Ural Bomber" requirements, but it, like the Ju 88, was caught up in the dive bombing craze. And while the Ju 88 ended up falling into a comfortable middle ground that produced a versatile airframe, the greater performance, range, and payload demanded of the He 177 would complicate things. Instead of four engines, which would provide too much drag for dive bombing, the bomber needed two engines that could provide similar power. Unfortunately, the engines that met requirements weren't readily available - those that did take shape would push the limits of Germany's capabilities and would plague the He 177 through its career. Development difficulties would constantly delay the program, meaning it wouldn't begin production until early 1942, and production would end with little over 1,000 aircraft produced.

Ultimately, the He 177 would be a fairly capable aircraft, despite the development problems and ongoing serviceability issues, and compared to the B-17, the only thing it was really behind in was defensive armament - it was faster and could carry a heavier payload over a similar distance. However, by the time it was in service, Germany was no longer focused on strategic bombing, and the demands of the Luftwaffe were being stretched thin to fly tactical support on the Eastern Front and defend the Reich at home.