It depends on the part. Since Apple doesn't sell the SSDs independently, it's hard to say exactly which way would be best here. For the last video card upgrade I did on the Mac Pro, I went through Apple direct, as their cost wasn't too far off other similar cards on the market. Buying through them meant my warranty is still honored from one source on anything in the system. Plus, it was the only variant of this video card with a mini displayport connector on it, handy for the (finally released) 27 inch monitor I bought.