Well the best tasting potato is one that was cooked with meat in a stew/potjie and sucked up all that sauce into the potato.
The better question would have been what is the best potatoes to use.
These white clean shyte they sell a the supermarkets are horrible
The day you realize you buy the darkest dirtiest looking potato and go taste the difference is when you know how you have been fooled your whole life. The closer you can get this this the better