For me, it’s Johnny Cash and Dolly Parton. I chose Cash because his is the Voice of God, and I chose Dolly because I don’t believe I’ve heard any sweeter voice in any genre of music, ever.
Close runners up for me included Merle Haggard, Willie Nelson, and George Jones for the men, and Loretta Lynn, Tammy Wynette, Emmylou Harris, and Reba McEntire for the ladies.
You?
Willie and Dolly.
Patsy Cline. Willie Nelson.
That’s a “Crazy” choice!
I’d go with Willie and Dolly, with Johnny & June a close second.
I’ve got to go with Merle and Patsy. There are more accomplished singers out there, but no one sings country like those two.
Willie and Emmylou.
Patsy Cline/George Jones
Don Reid (of the Statler Brothers) with Charlie Rich a close second.
Female vocalist is very difficult for me. Based on the content of my iPod, I’d say Amy Grant but I just can’t give it to her. I’d also have to give a nod towards the much under-rated Crystal Gayle but when all’s said and done, I have to give it to Reba. I’m not necessarily the biggest fan of her choice of material but she’s not afraid to get out there, loud and proud, and do them the way they need to be done.
Patsy Cline and either Don Gibson or Dwight Yoakam.
Emmylou and Townes (if he’s not country enough than Johnny).
Patsy Cline and Johnny Cash
Honorable mentions: Hank Williams, Patty Loveless, Willie Nelson, Loretta Lynn, Dolly Parton
Same as the OP, Johnny Cash and Dolly Parton.
Runners up are Willie Nelson, Loretta Lynn, June Carter Cash, Tammy Wynette, Patsy Cline and Natalie Maines.
Johnny & Patsy
Patsy and Hank Williams. I love Johnny Cash, but Hank…
Yes, Hank Snow.
What, no Kenny Rogers? Him and Dolly, especially the two of them doing “Islands in the Stream.”
Keny Rogers is country?
Well played! 
I prefer Hank Williams, but Snow was critical in the path of the genre’s evolution…
I wouldn’t really count that as a country song. Dolly’s done a few different genres, I’d lump that in with her “pop” recordings.