Those purple taters are very, very good keepers and excellent eaters as well! So you are well advised to save some for planting next spring!
The very best eaters I have found are the finger potatoes. They are small and white and look like little fingers, elongated sort of... if you can find them in the garden store or wherever, do it!
I hope to keep some for next year. I also bought some Colorado Rose, a red potato w/ white flesh, last spring. The eyes were barely visible on them and they never sprouted. Disappointing but I might buy some other variety next spring such as those yellow fingerlings. Space permitting. I could have planted four times as many PMs from the pound of seed potatoes they sent me.