I too used to be an off-roader myself and I agree with Tony, you need high quality screws that have high tensile strength and don't strip. Right now the only affordable and practical material is tensile steel. Oddly, stainless steel just isn't as good.
That doesn't mean you can't use Titanium though. For the bottom of my MTX-4 I use tensile steel Hexcrews (http://www.hexcrews.com
) but for plastic-plastic or carbon-plastic in the 3x8 to 3x10 range on the top of the car, servo holders, covers, etc. I use titanium. It's light which is what I want to keep weight down and keep the car agile. It also allows me to move weight where I need it (e.g. low centre).
Another thing to keep in mind is material alone is meaningless unless it's backed up by a company that knows how to handle it. If one set of screws says 'Made in Japan' and another says 'Made in China' don't you have a tendency to pick Japanese made because of their reputation for high quality?
The point here is, not all Ti, stainless, or whatever screws are the same. All of these materials are a combination of metals. How the metals are mixed, heated, and cooled affects their quality greatly. One bad experience with low cost Ti screws doesn't mean all Ti screws are crap. Go with a higher quality brand.
I wonder if anyone has made screws from Beta Titanium? That would be really awesome as a material for screws but I would guess the price is so outrageous that no one would even go to the effort.