Which is stronger

I prefer a Dana or Ford 9" for a drag car and I've never broke either one in 9 second 1/4 mile cars but you can make an 8.75 live with the right parts. If you back-brace it and install Mark Williams caps along with a spool, I've seen this setup run 8.80's in a small block Demon on spray.
Also, there are gear ratios for 8.75 rearends that tend to break easier than other ratios but I forget which ones. I believe it was MobarBilly on moparts that explained it to me in the past, he runs 8's and 9's with an 8.75.