Well still didn't played all possible sides of all scenarios, but pretty much every scenario I've played so far can be win in the same way.
First thing of all I decide how large perimeter I want to defend. Of course preferably the bigger the better (more income), but that is not always possible depending on a side... Sacrificing some isolated planets is required price of such approach. At key locations I always keep very large fleet, fleets which pretty much cannot be defeated by AI. My offensive arm are fighter squadrons. IMHO best fighter in the galaxy bar none is Furion. It can chew through everything. For Empire of course Tie-Defender. With Republic/Rebels it gets a bit dicey because to efficiently deal with capitals 2 fighters types are required.X-wing can do a lot of damage in a swarm, but swarm of B-Wings will obliterate everything... except enemy fighters. Now on routes where I want to expand just spaming fighters. There is nothing AI can throw against 100 Furions/Tie-D and survive (offense&defense alike). Defeats are rare. Got stuffed couple times but not because of superior AI but because for example pack of Lancer frigates parked under Golan platform and it is not possible to target that scum before obliterating Golan platform. And when dealing with defense platforms fighters are ripped to shreds.
If anyone want to have fun with 'fighters first' policy word of advice - target all anti-fighter units ASAP or die. Corona frigates are truly nasty opponents!
When defending a planet with enough fighters I always keep same routine when dealing with big guns: 1. Destroy Engines. 2. Destroy Hangar. 3. Obliterate target 4. Find next victim and repeat 1-3. Works every time... except some ships without Engine(s) HP he, he.