No experience with named/cultivated varieties, but I bought plants of seven varieties this spring from the nursery source linked below.
Nice folks, nice plants, very reasonable prices.
There's a link to a good MU extension publication on elderberries at their website.

Here is a link that might be useful: Elderberries @ Botany Shop

This post was edited by lucky_p on Fri, Jun 27, 14 at 14:43

OK. I've been reading more about them and I see why they're paired like they are all the time. Johns and Adams are taller, 10 to 12 feet. Nova and York are smaller, 6 foot range. Since you should buy different varieties to cross pollinate, it makes more sense to have varieties of like sizes so they look "right" when they're near each other. Johns has the larger fruit of the 4 mentioned.

Otherwise, I'm not sure there is much difference other than when they ripen. Adams ripens about two weeks before Johns. Nova ripens before York. But I haven't seen any relationship other than between those pairs.

They're supposedly not good raw and might actually cause a little digestive distress if too many are consumed raw. They either have cyanide or something like cyanide in the fruits. Once cooked, that goes away.