<<"Slowpoke, i will consider coming in mid-July.">>
If you have complete flexibility, most of us find September to be the best month to visit the region. Crows have diminished after the Summer rush, the eather pattern tends to be - on average- the best for sightseeing, and the hotels and other touirist services are all still open before the late Fall break.
The weather is quite different in the high Alps, compared to the lower areas, such as Luzern or Zürich.
<<"By "diverse" I meant valleys, meadows, peaks, lakes, waterfalls..">>
It's all there in the Jungfrau region. ;-)
The Lauterbrunnen Valley is called "The Valley of 72 Waterfalls."
In the attached picture of the Lauterbrunnen Valley, taken from if you look carefully at the cliff on the right, you will see a very fine (narrow) waterfall. The picture was taken in the Fall, or perhaps late Summer, when the flow is not at its peak. That occurs during the snow melt....May, June, early July. That particular waterfall is nice to look at all year, of course.
A very nice view of the lakes from high above is at Schynige Platte.
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Also, from the Brienzer Rothorn, close by the Jungfrau region, at the other end of the lake from Interlaken, there is a spectacular view of the lake ( der Brienzersee, Lake Brienz) with Interlaken in the distance.