That depends on if you want "new" country (as some are calling what's popular now) or "old" country.
Compared with other music genres, country music fans accept change much more slowly, so you hear some grumbling that today's country music is too "rock" or "pop" sounding. But that's just how life goes, things change, tastes change, technology changes.
Personally I like it all, whether it's Carrie Underwood, Kenny Chesney, Eric Church, Dierks Bentley, Miranda Lambert or Conway Twitty, George Jones, George Strait, Loretta Lynn, or Johnny Cash. (I have to admit I'm happy that Garth Brooks and Shania Twain are on hiatus, I got rather sick of hearing one of them on the radio every 10 minutes.)
George Strait, who is still very much making records and doing shows, has more #1 hits than any artist in any genre of music. He's a good place to start with.
George Jones is one of country music's "Gods." His song "He Stopped Loving Her Today" is arguably the best country song ever. But he's had lots and lots of other hits and did many duets with Tammy Wynette.
Loretta Lynn is perhaps country's top female vocalist of all time. Patsy Cline might have had that honor had she not been tragically killed in an accident many years ago before she really hit her prime. But she left us several great songs.
I have to say that Garth Brooks has probably played before more people in his concerts than any other country artist and he pretty much ruled the country charts in the 90s.
Martina McBride is the reigning Country female vocal queen with her powerful voice and emotional songs.
Carrie Underwood's career has blasted off like a rocket since her American Idol win.
Miranda Lambert has a great country music voice with her Texas twang. She is a great song writer for such a young woman.
Taylor Swift, at just 16, wrote or co-wrote all of the songs on her debut album (that just went #1 in Billboard's country charts.)
Kenny Chesney is selling out huge arenas on tour and is the modern equivalent of Jimmy Buffet with several songs about sand, surf, and bare feet.
Keith Urban, from down under in Australia, has had several chart topping songs and plays a mean guitar.
Brad Paisley has also recently had several hits and is another excellent guitar player (and a local boy from my neck of the woods.)
Alan Jackson has had a long and successful career with alot of hits and is highly regarded as a song writer.
The duet of Brooks and Dunn (Kix and Ronnie, respectively) has had a virtual lock on the best vocal duet category in the country awards shows for over a decade and two greatest hits CDs full of great songs.
Dierks Bentley and Eric Church are two up-and-comers with alot of success and radio and video airplay. Eric sings about the common, working man. Dierks has girl-appealing curly hair and a dog, Jake.
I could go on another four hours and not scratch the surface. Country music, whether it is "modern" with it's distorted guitars and daceability, or mellower classic country, always has one thing in common, the songs are about "truth." The songs are about and for real people. Hard working, Mom respecting, beer drinking, God fearing people.