I always prefer vintage or supporting designers, but I can never find pants in my size. Most vintage pieces are small in size because women were much more slender in the past. I would say maybe around once or twice a year I would venture out into a fast fashion store.
The key to buy fast fashion is to NEVER EVER buy anything with prints or graphics on them because you will end up being in a place with another girl wearing the same thing; always choose basic tees or bottoms in solid color.
Top: vintage from The Bargain District
Shoes and earrings: Dolce & Gabbana
Bag: vintage Gucci