While I highly recommend russet potatoes because of their high starch content, you can definitely use other types of potatoes. Different types of potatoes will result in different textures - textures that might also be equally delicious! Take note that potatoes with low to medium starch content will yield lumpier or creamier results, while potatoes with high starch content will have fluffier results.  You can also use different sizes depending on how you want to serve your smashed potatoes.