Honestly, the potato itself is only 50% of the story. The other 50% is butter. And I mean real butter, not that margarine impostor. Use warm butter, not cold. It makes a difference, trust me.
Also, warm your cream or milk before adding it. Cold liquid shocks the potatoes and makes them grainy. Nobody wants grainy mash. That’s a sad, sad dinner table.
Add the fat slowly. Taste as you go. You aren’t making a science experiment. You’re making comfort food. Let your heart decide how much butter is enough. (Spoiler: it’s never enough.)