When I am upgrading cars, I often see quite a few choices for Aspiration conversions, such as turbo/twin turbo or superchargers. When you have a choice between different aspiration changes, what determines what Aspiration conversion should you use, if at all?
Depends on what you need the car to do. Generally the centrifugal supercharger works great on all cars and was a must buy in previous forzas. The waters are a bit murky now. Some cars are turds with the supercharger but shine with the turbo.
Other times a conversion is unnecessary if the car really only needs handling upgrades due to high stock power figures.
It’s trial and error from what I’ve seen.
Yup, if you want to make the best car possible you need to try each one and run some laps. The lap times will give you the answer.
Turbos:
positives- more power, lighter weight
negatives- turbo lag which can cause wheelspin
usually the twin turbo is a better option as it has less turbo lag but creates the same power
Supercharger
positives- even power delivery
negatives- less power, more weight
Overall, the supercharger will be easier to drive however if driven to their max the turbo will usually be faster.
If I had to choose one it would be centrifugal every time.
From my experience I’ve found that superchargers are great for adding to acceleration whereas a turbo is good for top speed, so with tracks that have long straights I’d recommend the turbo chargers, for tacks that have a lot of turns etc go with a supercharger; like another poster already said turbo is lighter but takes time to spool, superchargers rely on pulleys to bring in forced induction.
Superchargers also have a more linear power delivery when compared to the turbo.
On tighter, twistier tracks where you go up and down the revs a lot a supercharger may be more beneficial.
On tracks with more straights and/or high speed corners where you don’t have to go in and out of boost a lot a turbo might be a good way to go.
As has been said already, the choice of upgrades depends most heavily on the car and track combination.
The thing is you get a lot more bang for your buck with the centrifugal. I’d always use the centrifugal if the car reaches the class limit no problem.
I’ve always preferred superchargers over turbos because of the even power delivery and i like the sound 
but there is a third option. Some cars don’t need a turbo or a supercharger because they drive fine how they are… In fact if you put some sort of forced induction on a some cars, it ruins the balance. For me the 458 is a prime example. I tend to only mess with that stuff of I’m in desperate need of looking for more PI