Like many kids learning the game at an early age (6), I loved the Knight. Hopping around like no other piece can and attacking most everyone else without being attacked in return. And the King/Queen fork! I always, still do, turned them sideways so I could see the handsome profile.
But I have grown to prefer the Bishop and especially the Rook. The long range of these two types outweighs the jumping of the Knight for me. Two Rooks linked and working together on a file or rank is a thing of beauty and power.
Of course the correct technical answer to your question is, 'Whatever piece works best in the postion in front of you.'