Well I tend to have typical scount ships and so on, but the combat fleet roughly looks like this:
Destroyers of various kind
Recon-Assault (Scanners, some laser/menson weapons) normally around ~8000 tons or less [Really just scanners, a little extra fuel to share, sometimes a bay for a fighter or more likly a laucher for scanners)
Missle Base/Destroyer ~ Loaded with todays choice of missles, mostly at least one oversized laucher for long range and some smaller ones for mid/short range, the big laucher drops a drone or other slow-but long range weapon that then explodes into a casset rocket/missle at the things detected by the scanner drones.
Then a Destroyer Leader, often with a good admiral and fancy name, up to 16 000 Tons, oversized guns, death ray lasers - but often a copy of another Destroyer Design that has proven useful, with double plating, extra engines and spare targeting systems.
For "roleplay" reasons, I have a jump engine on every ship. Maybe even self handicap.
As the game goes on I tend to run into the swarm which doesn't care much about my missles, at that point I normally make a dedicated PEW PEW PEW FAC ship that just runs in and shots everything with a stupid amount of high speed-tracking turrets and a angry crew. They often have to be towed back to earth after a long day of suicide rushing, double fire systems are standart - so no mather what blows up, they can keep shoting. Rarly over 5000 in size.
The introduction of smaller ships is then often followed by finally using that one lane i just had on "increase size" till now - A Battleship/Dreadnought, well over 10 000, often twice that. Normally cheap Material, Railguns, mensons, 80 CM Death Ray (I imagine it in the typical turrets ontop, death ray out the front) kinda design, a lumbering, useless, missle soaking monster stuffed with automatic defense systems and enough crew to fill a city with. Its a waste of resources, but damm do I love em... and those things tend to never die either.
Another often used, little liked design is the "Radar dish the size of a moon" - a huge scanner, some armor, some CIWS maybe and its done. Provides Active Sensors, while the destroyers normally have Heat/EM and smaller Active (Mostly active only for there own engagement range and size).
Then I normally feel really cool and proud that I won everything so far and the game didn't loop into errors yet and build the
"Sleek, fancy and awesome" Destroyer Design - Expensive little things under 10 000 - with stealth engines, medium armor, box lauching middle to short range missles, one or two one-shot Scanners and crazy fast engines. They sneak up to the enemy (often found by the moon sized radar dish), close into firing distance and then release as many missles as I can before I hit overflow errors. If needed, they bombard the enemy with scanner drones, followed by enough missiles to block out the sun.
If the game did not loop into errors by now, I normally let go of all restrains.
The MOTHHAARSHIP
Is it a planet? A sun?
Being well into swarm mother size (60 000) this baby shows up then releases a endless swarm of fighters, bombers, dogfighters, menson pokers, high speed middle delivery systems of various designs that will simply blow up anything smaller then 5000 and the bigger things get locked down with microwaves and menson, while it starts shoting fighters at your general direction that slam into your ship in return and force drop pots full of angry marines up your behind. Then it floats off to suck some fuel out of a gas giant and tow it's new baby home. If I feel like playing swarmy I disassemble the victim and turn it into more ships.
If the swarm would build bomber/fighters like I do (50x box lauchers can easly fit onto a single one, still with nice speed and depending on your rocket tech easly doing 50x16 damage) ...
And then it normally loops into endless errors, if it didn't before.