Konigsee vs Zugspitze

I went to the top of the Zugspitze in 1988. I have no plans to ever go up again.

I've taken the cruise on Kögigssee three times since 2000 and might go again.

'Nough said?

If you really want a mountain top view of the Alps, go up to the Kehlsteinhaus (Eagles Nest) or take the Jennerbahn, both in Berchtesgaden. They're not as high as the Zugspitze, but the view are quite spectacular, too. At one area where I used to ski in Colorado, the parking lot at the base was higher than the top of the Zugspitze.

You may be able to do the Jennerbahn cable car and the Konigsee boat trip in the same day. The Jennerbahn is next to Konigsee.

I'm the opposite, as we did the Konigsee boat trip once and weren't overly impressed. Pretty, but once was enough. Liked the Zugsitze a lot.

To try to answer your question, the Konigsee and the Zugspitze are not alike. Totally different perspectives. Being on a lake looking up and being on top of the Zuspitze looking down and all around.
What I'd do with the time you have, the Jennerbahn (instead of the Zugspitze) and Konigsee in a day.

Maybe I'm a bit jaded. Having viewed the world from the top of Pikes Peak, at 14,114 ft (4303m) and Mt Evans (parking lot) at 14,130 ft (4308m) and ridden my bicycle at 12,183 ft (3714m), a mere 9768 ft (less than 3000m) doesn't impress me.

I don't really need to hear the trumpet echo again, and St. Batholomä is not that impressive, but the Obersee, at the far end of Königssee is absolutely gorgeous.

Maybe Lee. We've been to the top of the Jungfraujoch and Gornergrat in Switzerland and still liked the views from the Zugspitze. To each their own.

I think it depends on the weather. Königssee fog and rain could be sunshine on the top of the Zugspitze. To get to the top of the Zugspitze is not cheap. Good weather I would opt for Königssee and the boat out to St. Bartholomä and beyond, unless you want to see snow and Alpenpanorama (depending on the time of year). Sitting in the sun on the Zugspitze with a Bier and a Bretze watching skiers in sunshine is something unique too. Plan last minute on the weather if possible would be my recommendation. Your days could have bad weather at both spots and go with a town/s or other sights. View the webcams and be flexible if possible. Have a plan B. Height is relative and it is the Alps that you traveled to see?

I would say that Lee and Paul have answered your question perfectly - you can't go wrong with either; it's really a matter of personal taste.