it's actually dependent on how the Imperial's deploy their starfighters, if the commander holds the TIE Fighters close in to screen his ship, he prevents the rebels from using TRD(Trench Run Disease) on his ImpStar and subsequently allowing the ISDs big guns to scatter the enemy snubs so the TIE Interceptors can use their superior speed to fall on the reb fighters while they break away and get behind them. Then two squadrons of eyeballs(TIE Starfighters) assist the Squints(interceptors) leaving one squadron to screen the TIE Bombers on their attack of the MC 80 which also allows the Impstar freedom to engage it.
It all really depends on the commanders involved. Though if you look at it from a straight statistic point of view(non biased this time) then you get the following
2 to 1 fighter advantage(yes the NRs have shields and torps but with the exception of the A Wing the TIEs have them beat in maneuverability and speed whic can be deciding factors)
3 to 1 firepower advantage(this also factors into damage it can take too as with more surface area and armor it takes much more killing)
Much higher troop complement. Assault shuttles could enter play and the Imperial marines could board and overwhelm rebel ship complements.
Bottom line, the Imperial Star Destroyer is a superior ship.
The Imperator is also easier to repair.
However, with regard to shielding, once the Imperial SD's shields are drained.... the generators become an easy and obvious target (if they have not already been destroyed).
Whereas the MC80 may well be able to retreat from the main battle, and recharge its shields (provided another ship draws the Impstar's fire away), and then re-engage in the battle.
Both can be argued to be extremely powerful vessels, whichever one may be be slightly superior.
