Bottom line the 9" is stronger but it is also heavier and harder to find in narrow widths. The 8" is a good solid rearend for most applications.

In a lot of cases the 9" gives you bragging rights but is overkill in many street applications. If you are running a combination that sees a lot of abuse such as a stick car or a car with a high stall converter and an engine with a lot of torque and sticky tires the 9" is the way to go.

No rearend is "bulletproof" you can break anything if you try hard enough.

I'm running a 9" in my wifes 77 Cobra II with a 302/C4 combination strictly because I had it laying around and for bragging rights. I'm running an 8" in my 77 Mustyang II coupe with a 351/4spd and don't expexct any problems from it even with the bigger engine and stick.

I've had good luck with both Auburn and Richmond. The key is to have them properly set up when you build the 3rd member.