Without a doubt Rozanne. Patricia is not far behind.

'Rozanne' :-) I bought 4 in bloom in June after reading all the comments here. They have been blooming non stop and still going strong. The one in partial shade is doing much better than those in full sun. People complained that she flopped. I won't mind that at all. I like floppy and sprawling plants.

My 'Patricia' is 4 years old and has not bloomed much at all. Only a few flowers a year. She was planted only a few feet from the best performing 'Rozanne'. I will get more 'Rozanne' next spring. :-P