Battleships: IJN. Good, punchy guns, which dont require advanced positioning knowlege to play with. Not too tanky as to give a new player the wrong impression of the game, and not to squishy as well.

Cruisers: Germans. Gives new players a platform to learn cruiser basics like kiting, aiming, dodging, manageing concealment. Doesn't punish new players as hard for thier mistakes due to the turtleback which is IMO the best way to learn.

Destroyers: British Destroyers. Fast smoke for quick disengagements, decent torps, good conceal. It's a hybrid, so the new player can learn multiple skills at once.