I use small ships only as PD interceptors - early in the game I make even my missile boats use larger hulls because of space efficiency (but of course I don't give them combat scanners or much other defenses.) Think about it, between an escort and a frigate you can get 50% more space for another pair of missiles pushed around by the same engines. The only thing to worry about is that if an enemy takes down one of your ships, you're out that much more firepower. But you still can field more firepower with the same resource investment if you play your cards right, so bigger is very often better. Late in the game I don't use missiles because large "tank-like" ships with huge guns and strong defenses can overpower anything using missiles (so can fighters if the enemy uses missiles with no point-defense cover.)
Many players specialize their ships, so you won't see a repair or supply ship with weapons very often, for example. Some will specialize their warships to work at a certain range for example. I prefer most of my warships to be effective at any range the enemy chooses to fight, so I tend to give them both long and short range weapons. Some will use troop transports with heavy defenses. With cargo III technology, devoting 80-100 kT on a large warship to cargo bays can allow you to carry ground troops into battle without worrying about defending transports. Better yet, I have an "armored dropship" design (large transport hull) that can survive running through most weapons platform defenses to unload its troops without damaging the planet. I also specialized a "meatshield" ship which is pretty much a giant floating gob of organic armor with engines to run ahead and absorb enemy fire. That was pretty much just for fun.
You should be aware that in strategic combat, PD ships will run away if they don't have at least one main gun (I'm pretty sure that's why it happens) and you need to play with their strategy a bit to make them hunt down the fighters and missiles before anything else and cover your other ships. This is a good example of specialization that will save you room on your larger ships for more guns.
[ December 04, 2003, 13:23: Message edited by: Nocturnal ]