If you're only going to grow one potato, I recommend growing our new potato - charlotte. The home grown flavour is outstanding.
If you'd like a potato crop to follow on from Charlotte, Valor is an excellent choice. Importantly, it has good resistance to 'blight' - a disease which attacks a high proportion of potatoes grown later in the year, turning them to a black gooey pulp. Valor also has very good storage qualities making it ideal for harvesting and keeping through the winter.
In case you were wondering - the picture's of a potato flower. When you see these you know the potatoes underneath are ripe and ready for digging!