As far as I know they all taste the same. I have a good recipe for a dahlia bread that's similar to zuccinni bread & quite good if you add enough cinnamon to it! I don't think they taste good as a veggie- bland & somewhat astringent.
They were originally taken to the old world- Spain -from the new world- Mexico -as a veggie but didn't make it as food just as flowers!

Weaver decribed the edible dahlia as a double-flowering red variety cultivated by the Nanticoke Indians of Maryland, 100 or so years ago.

Beth Hanson in the book "Buried Treasures: Tasty Tubers of
the World" pages 38-39 lists all 30 species of the
Dahlia family as edible. She does state that Dahlia
imperialis, the Imperial or Tree Dahlia, is used as
food in its native Central America. It grows to 15 feet?
Wow! How many tubers can such a large plant produce?