While either works fine, it seems like the preferred option would be to have an up and down arrow at both ends of the scroll bar. The solution is a little application called Prestissimo by PolyMorph Software. This little freeware application can instantly make you more productive by giving you that option. Modifying scroll bars is not the only thing that's up Prestissimo's sleeve. If you love the idea of hitting the Command-Tab keys to switch among different applications, but wish it was some other key combination, then open up Prestissimo.
Users can map to a variety of keys.
We love Command-Esc key combination since the Esc key is rarely used on the Mac. Another trick that Prestissimo pulls out of the hat is customization of the Application Palette when it is torn off the menu. Users can choose whether they want the palette vertical or horizontal, where on the screen it should be anchored, in what order the icons should be listed, large or small icons and whether or not the title bar is visible. If you sweat the details, you'll fnd Prestissimo invaluable. Prestissimo works on Mac OS 8.5 or better.