There are hundreds types of potatoes around the world, but most chefs agree that the best potatoes for mashing are the starchy types.
Depending in which country you live in, there are different types that are suitable.
Just to give you an idea in Australia go for Coliban, Dutch Creams, Golden delights, Sebago.
In the USA select Russets, or all-purpose potatoes like the Yukon golds.
In the UK Maris Piper potatoes seem to be Jamie Oliver's favourite for mashing, another one is Desiree.