Hi!
What do you think is the perfect ratio of fighters to bombers and why?
End of quote
Depends. 
I prefer fighters more, because they're more usefull: they kill bombers and ships with light armor significantly faster than bombers can kill other ships.
I look to see what ships make up the enemies fleet and adjust accordingly.
End of quote
That's exactly what I did in my recent SP 1.05 game. In my defensive hangars I used to equaly mix fighters and bombers, and it worked quite well for killing those ships AIs sent to scout. But when they came with 20-30 carriers, I just didn't have enough fighters to parry their bombers _and_ siege fregates, and also not enough bombers to harm other ships. Their fighters removed my bombers in the first minute, and my fighters in next 3, and their bombers and ships destroyed my orbitals in next 5. Even the usuall 4 repair bays and constant rebuilding didn't help much. I had to return my main fleet that was attacking their planets.
So I changed my hangars to have only fighters, and my planets under siege lasted _significantly_ longer - usually so long I could destroy a good number of AI's planets before I had to turn back to defend the planet under siege.
BR, Iztok