I need some suggestion...

[Escaflowne]

In general using the larger ship sizes is better for several reasons:

First, you can mount bigger guns on them by using larger mounts.
Second, you can mount more guns on them simply because they are bigger.
Third, they can absorb more punishment then smaller ships.

I generally use missile ships until I get to cruiser sized ships and then I usually switch over to direct fire variants. Mainly because by then the computer is using larger ships with decent point defense so the amount of missile I have to use to kill one ship is rather annoying.

However, when you switch over to direct fire variants you lose the range advantage over your enemy. Usually this is not bad since you more then make up by being able to fire every round or two. However against psychic races losing the range can be anything from a slight annoyance to nearly lethal if they steal lots of your ships.

My usual computer stomping ship is a dreadnought with a Master computer, best engines, either quantum reactor or some additional supply ships, 3-4 shields, 3-4 point defense, 8 heavy anti-proton beams, and some stealth and scattering armor. Add in the usual scanner and ECM and just sen in a a few fleets. They make short work of the computers. And they work against anyone.