August Frost is one of my favorites, its inexpensive, blooms late, blooms alot for a long time and has perfect blooms for me. Diamond dusted and nice substance. thick scapes that hold up well and increases quickly.
Joan Senior was a heavy bloomer for me and forms a clump quickly, almost too quickly -if you are one who can't stand yesterdays blooms hanging on and like to dead head-this one will drive you crazy, because it blooms so much at once that it is a real job to keep deadheaded. It was pretty white for me, not too yellowish.