Country roads, nothing! That looks just like the highway running from where I live at least the first 4 or 5 miles of it. After putting up with this for several decades I’ve come to the conclusion there is no “best method” as both lanes are like that. It’s mostly wallow around, hoping to hit less offensive spots due to sheer luck, and beating every profane word, along with the car, to death.
That washboard is caused by poor construction practices; mainly grader blades chattering from taking too big a bit or going too fast.
Some graders are even running chatter bands on the blades but it doesn’t mean anything if they’re digging too deep and/or have the machine at top speed.
A brake rotor or drum being machined on a lathe will also chatter and have a coarse texture for the same reasons; too much being cut off at one time, cut too fast, and no chatter band being used.
The powers that be finally resurfaced the highway here within the last few days and it accomplished absolutely nothing. The roadway as of today still reminds one of driving down the railroad tracks; sans rails. 