What bus type is best for my GPU?

While looking around on various sites for the Sapphire R9 280X 3G 1100Hz Toxic video card I have noticed that there are variants of it.

These variants are the bus type.

Please see on the left hand side the different available bus types:


What is the best/fastest bus type for my card and what are the differences between them? Also what effect does the bus type have on the overall price.

The three bus types seen on the AMD site linked above are:
- PCIe x16 Gen 3.0

- PCIe

- PCIe Gen 3.0



-A very confused shopper.



Some sites don't list the generation of PCI-E and all modern cards are built for Gen 3.0 and PCI-E Gen 3.0 is backwards compatible with previous generations of PCI-E so there is no difference between "PCI-E" and PCI-E Gen 3.0 as they are the same exact thing

Thank you very much!