Mesa: gallium drivers versus dri drivers

The instructions for building mesa in BLFS 9.0 have suddenly become a lot more complicated. There are now configuration flags for both gallium drivers and dri drivers, but i915 (the driver I am most interested in) can only be built as one or the other. I have not been able to find any simple comparison of these options in practice. Can anyone enlighten me?

In previous versions, I used a gallium driver. My computer has an Intel Bay Tree processor with integrated graphics.