If in a position to get both (of whichever two you are considering), grow them together. Odds are you will like one over the other and can rehome the one you like less. Or choose a preferred bloom season to decide which to get. I tend to avoid those described as having a Mid bloom season. Just a couple of ideas.
Edited: Oh, yeah, and be sure to look at other resources for images. For example, ATP and the Iris twiki may show you that images in 'real' folks' gardens are enough different from the vendor's images that you can make an easier decision.
