It is hard to recommend a single artist as the best place to start listening to the blues. what I would recommend is a couple Albums by Various Artists:
Most blues music is characterized by the region of its origin. You have the Mississippi or south blues, and you have the Chicago or north blues. The north blues tends to lean towards a R & B sound with more electric guitars. The south blues tends to be more acoustic, bare bones type music, what I like to call the "dirty" south sound.
Then the blues is further separated by pre/post WWII. The older the blues, the more raw the sound (prewar).
Any Butterfield Blues Band compilation containing the tracks "Born in Chicago", "Walkin' Blues" and "Get out of My Life Woman". These all sound absolutely fabulous on a good stereo with the pounding bass beat behind Paul Butterfield's wailing harp.