what is the best way to invade planet defended by fighters?

Drop a few fighters with the troops initialy just load them on the troop transport. Re attack the planet with a cargo ship with fighters on if you dident manage it first time.

It also helps to equip the troops or some of them with small weapons as ground cannon are useless against fighters

I actually have resorted to ramming my troops into stuff to kill them... I don't know if you can ram fighters... If your in a posiiton where your weapons aren't damageing them, then sounds like you need to research better weapons.

I usually drop fighters with troops, actually fighters might be perferable. You can use them in space battles as well. Fighters are pretty much unbalanced super weapons and the carrier is not to be triffled with...

SEV, more than a feeling.

I think fighters need to be taken out of ground combat. One can pay for a troop, which is only good on the ground, or one can pay for a fighter, which is good on the ground and in space. Seems kinda a no-duh decision.

I have to disagree but then I hapen to like the combined arms feel of having to provide AA weapons or fighter cover and I build some fighters as ground combat vesels

I just send ships with PD and weapons that can target fighters and destroy them all. The ship at the very back is always the transport so its targetted last so it gets through.