Heh.
Probably a mix is best for most purposes. For example, ideally, the enemy might be trying and usually failing to swat your smaller ships, while your bigger ships pound them.
Smaller ships are much cheaper to maintain, and can be very difficult to hit, especially if the enemy only has big clumsy ships. The smallest (scout and escort class) ships usually can't hold strong enough weapons to effectively engage larger ships, but they can be used as raiders, nuisance ships, and support ships.
Frigates and destroyers can both be useful in fleets. They still lack the punch of larger ships, but can do meaningful damage, and are good platforms for PD, seekers. They can also serve well with regular weapons, giving the enemy the choice of either trying to hit them, or ignoring them and getting hit by them. They can distract a lot of enemy attention from your bigger ships. Their natural attack bonuses from agility mean they don't need as much ECM/sensor expense.
Bigger ships are still the most powerful, but in Proportions they cost more like what they're worth, or even more. Although they are more expensive, use lots of supplies to move, and are even more expensive if you try to make them fast, having the best and most powerful heavy ships can make the difference between victory and defeat in a large battle. The trick is deciding how big and how expensive you need to go to get an advantage, catching the enemy fleet with your superior ships, and making it all not so expensive you win one fight but lose several others.
There are also decisions to make about what level of components to use, and how much space to devote to protection verus weapons. For example, armor gets better and better at higher levels, but the cost goes up even more steeply. You may want to try large ships with cheap components, or small ships with expensive ones, in some cases. Unlike the unmodded game, armored structure makes a large difference in a ship's ability to absorb damage. A ship with 1/4 to 1/2 its mass in armored structure will tend to be able to take several times the amount of hits of a ship with just weapons.
Another approach is to have cheap and small ships on patrol during peace time, with large and expensive ships mothballed. Or, just keep a large resource reserve, plenty of shipyards, and build a new expensive fleet when a war breaks out. Then win the war before the reserves run out.
PvK
[ March 22, 2004, 21:24: Message edited by: PvK ]