Well, the version that you select depends on what architecture your processor is (x86 or x64). Generally nowadays, everything is x64 based as it allows for more RAM (>4GB, usually less). You say that you're running Windows 8 - and if that's 64-bit then your processor will be too. This is just to check, as it's quite likely it's 64 bit anyway. Head to the control panel and find "system" (you can search "system", and hit the first result.) There, if you're running a 64-bit version of Windows 8, "x64-based PC" is displayed in the " system type" field under the "item" heading.
So, go for the amd64 installation. The others are for other, differing architectures of processor - and most consumer chips are of this architecture today.