It depends on the type of garment, and how you plan to use it.
For example if you're buying tshirts, ring-spun cotton is ideal. Thicker and heavier the weight (gsm), the better. Quality stitching, see if it's double-stitched along the bottom, or if it's made by hand - backstitched.
Silk and linen will last longer, but you also need to be more careful with them. You can't throw them in the dryer. Cotton is good for casual wear if it's heavy gsm, ring-spun and has good stitching but silk and linen will outlast you and your children. Seriously, you can buy suits from the early 1900's that just need new stitching.
Blended cotton is made to be stronger, but will age weirdly if you're using a dryer. The tension of the different blends of polyester and cotton will fuck up your garment over time. It's also not suitable for exercise or if you sweat a lot. If you're just wearing it around the house - blended is a great choice - but you'll need to be careful as most blended garments are made that way because they're cheaper to produce and "feel good". So you'll have more shitty manufacturing practices to look out for.
There are great $5 t-shirts mass manufactured in Bangladesh out there, and there are shitty $70 t-shirts made by hand in the US.
White and Black is a good choice, as both can be dyed or bleached (start with oxygen-based bleach like OxiClean before trying chlorinated bleach on fabric) to look like new.
This is just t-shirts. Dresses and skirts, jeans, dress pants, shoes, everything else has their own specific instructions. Most of the time the manufacturer knows better than any guide you read online about the product, read the tags. And I didn't even get started on wool tshirts designed for hikers.
Oil stains aren't the end of the world. Starting with white tshirts and ending up with black (or dark-colored) dyed shirts is a great way to prolong the life of an oil-stained garment you can't get the oil out of.
Any other tips?