For the Empire I think fighters are still usefull. Mostly because they are free and with lots of them you can quickly take out enemy bombers. The Empire also has the benefit of fighters coming out of ships that can take out corvettes somewhat quick (though I think they should take them out even faster). A common tactic I use.
Just hyper in as much VSD and ISD type ships. Their fighter capacity is more than enough to take out any reasonable amount of bomers. The bombers can quickly take out any shield generators and hangars that might be there. After teh hangars are gone, the Fighters can go hunt all other enemy fighter size ships. Meanwhile the bomers take out weapons and once the fighters are finished they can join up with the bombers. The big ships can quickly destroy any other ship, due to their numbers. Single fighter squads also won't last against full SDs, their shields will recharge fast enough to prevent any damage. Every once in a while a fighter gets hit by a turbolaser and blows up right away. It may take a long time, but in the end you will win. It took me a whole hour once, but I did win and I hardly ever have any losses.
Folr the rebels, fighters are useless. Their bombers seem to do their job well, but the gunships can do the same thing only slower. Still the gunships can take much more of a beating so by using them I actually still lose less and I can get out with no losses. However if the gunship was to be armed with, say, guns (I wonder why they called it a gunship in EAW, at least TIE Fighter had them armed with guns) I would have a greater need for bombers for the rebels as well.