Jarod Cain, the Grey Fleet is yours. At the moment they're headed into Ferengi space to very covertly blow up Ferengi vessels and space stations. I'll put your flag on the Nautilus.
Haspen touched on the difference between the ships briefly.
- A Miranda class destroyer costs 1410 industry to build. That buys you 62 hit points, 220 shields, 4 phaser banks and 3 torpedoes. It's got a speed of 1 sector per turn and operates in the medium range.
- A Miranda class destroyer 2 costs 2660 industry, with 76 hitpoints, 280 shields, 6 phaser emmiters, and 4 photon torpedoes. It's got a speed of 2 sectors per turn and also operates in the medium range.
In addition to the enhanced hull and shields, the phasers and torpedoes deal more damage than the old model. And finally, the increased speed makes the Miranda an extremely effective border patrol boat.
The key here is that the upgraded destroyer 2 totally replaces the older models. All existing destroyers get automatically upgraded (at no cost) and we are unable to build un-upgraded destroyers from now on.
Constellation class Heavy Destroyers won't be available until several of our techs are level 6. They are an improvement over the Miranda in every way. Most notably having a speed of 3 sectors per turn, which is among the fastest ships in the game. But at that point I generally prefer to switch to Galaxy-X class Heavy Cruisers rather than keep building destroyers.
Defiant class Heavy Escorts are one of the last ships we develop, with some tech requirements at 10 and the rest at 9. They are absolute beasts, and have firepower superior to the Galaxy class Command Cruiser
2, though less hitpoints and shields. Also they are the fastest ships in the game, at a speed of 4.