The annoying thing with Amazon shipping is that sometimes you can't order an expedited shipping option if needed, even for prime items. This tends to be due to third-party sellers that participate in the prime program, but for some reason don't offer any other option but the free 2-day. There have been times when I've paid the extra for next-day air for some things, though it tends to be very expensive.
The larger issue is that I simply no trust Amazon to actually deliver. Between Amazon "accidentally" switching my purchases to something non-Prime and not actually having something in stock in spite of their claims to the contrary, I cannot count on any delivery date promised by Amazon.
If I need computer parts, for example, I'm going to Newegg because they will actually have the part and actually deliver when they say they will.
At least, that's what it seems like to me as a layman.