If you have been searching for a white rose that will stand the heat of summer, cold winters, and wet springs, 'Paloma Blanca', a 1984 Griffith Buck introduction, is a rose that you need to consider. Her name translates to "White Dove" in English, an apt metaphor for this beautiful white rose.
In my estimate, the factor that places 'Paloma Blanca' above other white roses is its staying power. I've always been impressed by how long a bloom of 'Paloma Blanca' will last indoors or out. I've seen garden clusters last for weeks in reasonable weather without fading or dropping. Other touted white roses such as 'Blanc Double de Coubert', or 'Frau Karl Druschi' may have better form, but they won't last as long on the bush and they'll be brown ugly sacks by the time 'Paloma Blanca' starts to fade. And the famous 'Iceberg' is a dud here in my climate, while 'Paloma Blanca' just keeps plugging along. Other positives in her favor are that she blooms her head off from the time she is a very small bush (see the photo below of a few months old bush) and that she never seems to fade to brown as most white roses do; petals seem to fall before they turn ugly.
'Paloma Blanca' is officially a white or near white Shrub Rose that has very double blooms (35-40 petals) but only a light rose scent. Those double blooms are large and presented in clusters, but I wouldn't try to claim that they have a classic Hybrid Tea form. They seem to start as fat buds and then "half open", displaying a little of the center for a long time without opening completely flat. The blooms are a very pure white for the majority of their time on earth, although at colder temperatures I detect a little blush in their petals and in some lighting the center can have a slight yellow tone. 'Paloma Blanca' blooms continuously.
My 'Paloma Blanca' is only one complete season old, but I used to grow her at my previous home and I can attest to both her winter hardiness and her foliage health. This is a very disease resistant rose. I don't have to spray 'Paloma Blanca' for fungus here. The picture at the left, taken just last week, is a bush that froze back to the ground last winter and has not been sprayed all summer. At full growth, she reached 4 feet tall in my old garden, a columnar rose who doesn't get very wide. Her breeding was a very complex mix of 'Vera Dalton' crossed with a seedling whose heredity included 'Lillian Gibson', 'Pink Princess', 'Florence Mary Morse', Rosa laxa, and 'Joseph Rothmand'.
In your search for a white rose, I hope I've convinced you to consider 'Paloma Blanca'. A White Dove in the garden is always a welcome sight.