geranium is sad
I have two geraniums outside on my patio. They are different in color from leaves to flowers. But they are similar because the leaves look the same. The geranium in question has gotten lots of rust and white on the leaves. The geranium right next to it is very healthy but did not flower much this summer even though I fertilized a few times. I wish I could send a photo, but I don't see where I can browse and attach one.
Plants are like people in several respects. Different varieties have different qualities. One of your geraniums is more disease resistant and more vigorous. The other variety is not as hardy. If all things are equal, even down to the potting soil, I would consider keeping the nicer of the two. The other could be treated, but if within 2-3 feet, could infect the 'good' one. Just something to consider.