I like music, but I'm not an expert by any stretch in other genres -- However, I'm a bit of a connouisseur of country and western, and I have to say, the answer to this question in the C&W world is without a doubt Kevin Fowler.
This guy's music, voice, lyrics are all superb - he's one of my top 3 or 4 all-time C&W performers/artists, and should easily break into almost anyone's top 15-20 list, if you're a fan of true country & western, not pop charading as C&W. Yet he's relegated mostly to the Texas circuit/charts.
For starters, here's one of the best songs ever:
http://www.youtube.com/watch?v=mCOLL8ZRddk
That one was a fullblown mainstream Nashville hit, as well it should have been, but a lot of other ones of his should have been, too.
How's about a little Lord Loves the Drinkin Man:
http://www.youtube.com/watch?v=V4Bvpd3aSZU&feature=related
I put Kevin up there with the likes of some of the legends, or close behind, but not many other people do....
I love Texas Country/ Red Dirt, that's about all I listen to, but Kevin Fowler??
I'd have to say Jason Boland and Reckless Kelly are way underrated, as is Stoney LaRue, Stoney has one of the best voices I have ever had the pleasure of hearing, he has had a 10 year career and only released 1.5 albums, because of his voice he can cover just about anyone.