You're asking about the most common situation. It is very much going to depend on the type of mouse and the device the user is using and more importantly, your type of content (see below).
I know there are touch screen, mobile and other device to consider, but really the question is specifically about the most common situation in which the OP's website will be accessed and that sounds like it's going to be a standard desktop.
According to Microsoft's own research, the qualitative results of their analysis of scrolling techniques shows that the ScrollPoint joystick mouse such as the IBM ScrollPoint Pro and accelerated mouse wheels (where the acceleration is a software setting in the OS, Browser, or device settings) that have a 'flick' type of action are good for scrolling long distances - provided it's set up at 3 scroll lines per notch in the case of the accelerated mouse wheel. Microsoft seem to suggest that 3 lines per notch is the default setting, and that's what I'm seeing on my machine right now.
However - ScrollPoint joystick mice and mouse wheels and associated wheel acceleration settings that afford flicking are probably not the most common type of scrolling environment. I'd imagine the commonest, by percentage, to be the standard (cheap) mouse.
Up down arrows, negative space, page keys are more likely used for local examination - moving back and forth from the current page in order to visually relate the previous or next chunk with the current chunk. A kind of progressive step mode.
With very long pages, dragging the scrollbar is commonly used to scan (visual search) or get an overview of the whole page - to determine its usefulness - a kind of 'see before you buy'. The longer the page, the more likely users are to reach out and actually drag the scrollbar up and down.
The more your content affords random access viewing as opposed to linear access, the more the scrollbar will be used. And that depends on your content and whether users are likely to want to examine the content in successive step mode - like reading a long single article (linear access), or to flip about, or get an overview - eg a collection of articles of which some are of interest, and some not (random access).
Also factor in whether your content promotes the beginning and the end pages to be of more interest to the middle bulk (eg examining first and last items in a long ordered list). In which case Home and End keys come back into play a bit more.
I'd recommend you try some user testing. It might be worth getting a few different users to actually use the website and either watch them, or gather statistics about how the user is moving about on your page: This article from superuser SE could help: Application to gather mouse usage statistics.