re: Merle Haggard & George Jones-A Taste of Yesterday's Wine

It's hard to narrow it down to a top 5 only. There's Lefty Frizzell & Buck Owens whom you've mentioned and there's Faron Young, Webb Pierce, Hank Snow, Charley Pride,

And some who came along a little later, Don Williams, Gene Watson, Don Williams, George Strait, & Hank Williams Jr. (mostly his earlier stuff)
Then there's the ladies: Loretta Lynn, Patsy Cline, Tammy Wynette...