Depends.  For defenses(hanger bays & starbases) it's typically fighter biased as the greatest threats to defenses are bombers & anti-module frigates(both of which fighters counter).

As a rule though late game, the standard play is to just mass bombers as they are one of the only frigate based damage sources that can be effectively be used against caps/titans once titans roll out.  Fighter could be massed too if you know for sure the opponent is planning to mass bombers and you're fairly certain your titan can beat their titan with minimal damage contributed by it's fleet of frigates(though to be fair once the enemy bombers are out of the air, even a swarm of fighters will contribute more damage to capitals/titans then the enemy's swarm of dead bombers).

Under most circumstances you are better of by bomber spamming yourself:

https://forums.sinsofasolarempire.com/438860

I'm aware of that thread....but what it didn't address at all is corvettes, which 1) aren't bad at shooting down bombers and 2) are countered quite well by fighters...

Excluding VL, titan/cap fleets are generally pretty vulnerable to corvette spam....early and maybe mid game you can use flak, but late game those flak frigates will get eaten by titan AoEs, caps, and SBs (it's mainly the titan AoEs)...fighters are your best way to deal with all those corvettes....

Assuming the next balance patch fixes desperation, I think it will become quite apparent that late game fleets have to be able to counter corvette spam, and flak simply won't be good enough...unless you pull off some MB magic, fighters will be the counter to corvette spam....