A few opinion's.....
The X3 is the best riding coach today, followed by the H3, then the DL3 and its derivatives, then the J45, and last, the Van Hools. The best ride of all time was the Eagle, especially on a really rough, potholed road, due to its IFS and exceptionally long 'travel' to absorb the bumps.
Agree with rickycourtney...maintenance can be a huge factor in ride...especially tires and their balance, as well as shocks, etc.
To me, the "decline" in GL was started when the company began large diversification, in the '60's, taking revenue from their core business, and putting it into more lucrative investments. Good for the stockholder's, but bad for the busline's employees and passenger's.
And then came deregulation and the end of the ICC. The resulting fierce competition for business by cut-rate carrier's resulted in cost-cutting measure's, end of 'cross-subsidizing' of secondary routes, and other negative impact. The taxpayer funded, government owned transit system's, who could pay their driver's much higher pay and benefits from the pockets of taxpayer's, and not just the farebox, resulted in the best qualified driver's going there for employment, rather than private carrier's.
And yes...the end of the CAB and airline deregulation resulted in companies like 'People Express' and other airlines taking much of the busline's traditional market share.
Even the resurgence of Amtrak, especially in California, also took a chunk of the market....