Actually, my favourite is always whatever happens to be in bloom at the time, but as I haven't tried growing Dutch Irises in a container before I'm very impressed at how strong and healthy they look.
When I am Rich and have my big garden I'll be able to plant great swathes of them (ooh, won't they look stunning!) but until then the advantage of only having a few is that I really notice and admire every little detail.
It's definitely a case of less is more ...
… and this one's going to be blue!