I've only tried one of the new DD missions so far but overall:
Favorites:
Both ironclad battles: Funny, and trying to find a solution to damage the enemy ship with low penetration was entertaining, used max penetration on monitor and max incendiary on virginia
German raiding squadron: Enjoyed having to choose between firepower, torpedoes, speed, and survivability to create small ships capable of sinking cargo ships in a timely fashion while avoiding the guns of their escorts
Dreadnought vs modern cruisers: Liked how distinct the enemy advantages and my advantages were; had to make full use of armor and gun penetration knowing the enemy ships had torpedoes and more accurate, but less powerful guns. Focused on maintaining distance while weathering their low caliber guns before finally landing devastating hits.
Modern vs old destroyers: One of my favorite custom battles was to create one modern destroyer and place it against 5 or 6 ai destroyers. Put everything into firepower, accuracy, surviability and sonar, making short work of anything that came within 3km while dodging the older DD guns.
Hurry up: Enjoyed creating torpedo boats capable of quickly reaching battle, dodging high caliber guns and torpedoes, and doing torpedo hit and runs.
Least favorites:
US Super Battleship: If I invest everything into firepower, the japanese battleships hightail away at warp speed before I can inflict sufficient damage until the timer runs out. If I invest everything into speed, the japanese battleships still hightail away at warp speed until the timer runs out. Also personally not a fan of 1vs large fleet missions in general.