Using a linear search to find a value that is stored in the last element of an array of 20,000 elements, 20,000 element(s) must be compared.
It really is hard to say because there are many slots and we do not know what your teacher is teaching. I have seen a lot of teachers teaching out of date material. With that said, here is a list from best to worst.
PCI Express x16
PCI Express x1
AGP
PCI
This is list is based on greatest to least and base on the bandwidth read and write speed.
Making guesses, as opposed to the other answers, this is the only one that forges new ideas and doing such will only lead to an illegitimate conclusion/study.