I would never be able to choose a favorite flower, but surely iris are in my top five!
I grow dozens of varieties, mainly blues and purples. I order most of them from catalogs which is a daunting task since they are all so beautiful. One year I just went through and picked all the blue ones that had names starting with the letter "A". I had planned on doing the "B's" the next year, but somehow got sidetracked.
Iris start blooming fairly early here, soon after the narcissus are done. I remember early one spring I was spending a tiring morning hauling down bags of amendments, yanking hoses around, swatting bugs and I honestly began to wonder why I was doing all this hard work. At that very moment I went around a tree and my breathe was actually taken away by the sight of the most beautiful blue iris blooming that I had ever seen. I hadn't even noticed it getting ready to bloom the day before. I couldn't even remember planting it. That answered my question as to why I do it - for moments that take my breathe away.
Note: I do realize that not everyone is awestruck by the sight of a perfect flower. Just the lucky ones.