Elderberry varieties

Is there a difference in the effectiveness of berries from different varieties of elderberry? I have planted a lot of standard elderberries in our hedging but also have one of the purple elders (Sambucus Nigra Black Lace) in the garden and wondered which to use.

There isn't sufficient research at this time to say, "hey this cultivar(s) produces consistently higher levels of these beneficial chemicals X, Y, Z, etc.."  

At this time, what matters more in my opinion is 1. soil 2. sun 3. sufficient moisture for producing the best quality fruit on an elder.  

I suppose this fits under this heading...what varieties of elderberry would be best suited to very cold climates, such as zone 2 or 3?

Laurie,
There is some debate here.  My book has some general zone guides, though I think in zones 3 and especially 2 it is quite hard to grow elder that have sufficient time to fruit well.  Aka, even if you get growth, you may get little to no fruit.  

My suggestion when trying to decide on varieties though is whenever possible, find someone in your area/region who is growing it successfully.  Nursery and plant guides are not infallible, and I have often been surprised to see a grower doing something that those resources said was not possible/applicable!  

General hardiness for canadensis is 3-7, but it does best in 4-7.

Thanks. We are considered zone 3.

I know of nobody growing elder here. I imagine someone has tried, however, as a big box store was selling the "Black Lace" (a proprietary variety anyway) cultivar.

We have plenty of moisture - that certainly isn't a problem, but it isn't very sunny here (Highlands of Scotland). Would that make any berries grown here less effective?

No, not less effective.  A good rule of thumb is to try and find someone in your area successfully growing a plant you want to grow. Know anyone in your region growing elder?  

Zone 7b here!  This is very good news to read that Elderberry will grow where I am.  I have been using Elderberry throughout this cold season, but would absolutely love to grow my own.