DISCLAIMER: This is MY opinion and does not reflect the opinion of Team Associated or any of my "teammates".
When it comes screws/fasteners in R/C cars, I rate them in the following order:
#1 Titanium. Nearly as light as aluminum. As strong or stronger than steel. Won't rust like steel. Adds a bit of bling. One caveat: There are some cheap grades of Ti out there to be avoided. Con: Expensive.
#2 Stock fasteners or quality steel. There's a reason steel is still used to hold everything from iPhones to fighter jets together. Con : Heavy, prone to rust
#3 Aluminum. Lightweight. Ideal in low stress locations. Will not rust like steel. Can be anodized to give you some bling factor. Con: Not very strong. Can react to some cleaners. Anodizing fades over time.
#4 Stainless Steel. Shiny. USUALLY doesn't rust like steel. Some grades of stainless can rust. Con: As heavy or heavier than steel. Not as strong as steel.