Bullet i just found this and copy and paste for you.
There was a mulberry tasting at the Wolfskill Experimental Orchard/USDA Germplasm Repository in Winters, last weekend, June 5, 2012. I will share a few thoughts by reviving this old thread.
Cultivars offered for tasting (to the best of my recollection ... I did not take notes):
"Illinois Everbearing"
"Pakistan"
"Oscar"
"Beautiful Day" (white-fruited)
Another white-fruit selection the name of which I can't recall.
"Rupp's Roumanian"
"Thomson"
"Kokuso"
Possibly "Shangri-La", although I may be mistaken.
(Some participants took good notes plus photographs, and perhaps one of them will correct my list.)
No Morus nigra selections were offered, as none were ripe at the time of the event.
The clear favorites of the crowd were "Illinois Everbearing" and "Pakistan". (The piles of fruit of those two cultivars on the display table were eaten down to bare plates very early.) They had the best sugar/acid balance, I think. To my palate, on that occasion, the only other cultivar that approached those two in quality (in terms of a bit of acidity to balance the sweetness) was "Oscar".
"Thomson", "Rupp's Roumanian", and "Kokuso" all tasted straight sweet, sweet, sweet to me. They were all large, plump, handsome fruits, and might be fun to grow just for some variation -- they were all pleasant to eat, if not quite as pleasing as the selections with some "tang" in the flavor profile.
I was not keen on the white-fruited selections.