What is the most effective ship combination when making naval units?

Currently, I prefer Battleships and a few escort subs for a major naval engagement ... To escort a small number of transports, I prefer either a destroyer or a cruiser ...

Thanks. I've been thinking about getting a few subs and destroyers to go with battleships so it's protected from submarines and other ships.

I usually dont make that many destroyers cause sub v sub but subs can destroy many other ships, whereas destroyers are only effective against subs and can be easily destroeyd by other units such as battleships. I also try to make some aircraft carriers, especially if I'm an island.

Battleships, Cruisers, and destroyers are fairly effective vs. air attacks ... I normally don't bombard enemy fleets containing those units unless they are engaging another naval fleet of mine or an ally ...