Technically this was the precursor to the 3-2-2-2 series of exercises. Patterns that have a two-note alternating line on top or bottom and a more active line on the opposite side seem to work real nicely. The two-note alternating pattern is easy to play on autopilot and then concentrate on the line on the other side. Notice how the top line starts on alternating notes and repeats every other measure.
Variation 1 just alters the top line to get a different tonal color.
Variation 2 shows yet another top line to achieve yet a different tonal color. In the top line, the single note E-natural, alternating with the double stop is quite a bit harder to finger for me than the previous version.
Variation 3 uses yet another double stop on top. This one is much easier to finger. When applying the chords and the chromatic approach notes in the bass you get a nice double turnaround function.