As you might be able to tell from the photograph, I love growing roses! Traditional advice makes them seem difficult to grow, particularly with all the pruning dos and don'ts but I ignore that, prune as and when I wish, and generally my roses flourish!
The rose in the photo doesn't have much scent but I do have others that are not so fabulous to look at but that have a glorious smell. I also have a yellow rose bush climbing through some ivy which I love. This doesn't get any attention at all and it seems to thrive on it.
Roses are definitely up there, and I agree wit you, Verity. They're easy! Hack the crap out of them at the end of winter and fertilise. They do the rest on their own! Lavender is also easy to grow, requires no pruning, and looks fantastic. Daisies and the daisy family .... the same. I like things that grow without effort and are bright and colourful.
My favourite flower would have to be the Sunflower. The very nature of its beautiful yellow and black face makes you smile, they are vibrant and full of joy. They are hardy in our environment and easy to grow. A great flower to introduce kids to gardening with - it is very hard to kill the old sunflower.