Can't honestly answer...but Satsuma is a really good tasting/sweet plum. It was my dad's favorite. It needs a pollinizer like Santa Rosa.

To some degree you are comparing apples and oranges, Satsuma is a rich-flavored red-fleshed plum and Shiro is a mild-favored yellow plum. Color plays a big role in the flavor profile, the all-yellow ones are more in the pineapple category and the red-fleshed ones are more like cherries/berries. Personally I prefer Satsuma.

Scott

I already have beauty plum. Does Satsuma taste like beauty?

My Beauty hasn't fruited yet (well it did last year but the critters got them all). However its a yellow fleshed red-skinned plum and those all taste quite a bit different than the red-fleshed ones.

Scott

Scott is very good at classifying taste differences in fruits without clouding things up too much with his own personal preferences.

I'm a more strongly opinionated type, I think, and I much prefer the flavor of Satsuma to Shiro. But I'm in the northeast. When Shiro is starved for water and really gets up top sugar it can be remarkably good, but I suspect in areas with likely ample rain during the growing season, Satsuma will be consistently more flavorful to most palates.

Birds are much more likely to leave Shiro alone, however.

To me, the Shiro is the best-tasting plum I have ever had! The animals stay away from it as it is yellow as well.