Being way too big of a wrestling fan until the last year or so (looking at my 6 binders with over 1500 wrestling DVD's) my pick will be a little different. My pick is "Beautiful" Bobby Eaton.
No matter where he went, he had a great matches. From the early 80's in Memphis as a solo work he had a good body of work. But his shinning moments were being one half of The Midnight Express. it didn't matter if it was the first version (with "Loverboy" Dennis Condrey) or the 2nd version (with "Sweet" Stan Lane) the team was one of the best. Their feuds with The Rock-n-Roll Express, The Road Warriors and The Fantastics are the stuff of legends. Even after this, he had a good career in WCW winning the TV title and being a large part of the Dangerous Alliance. He truly might go down as the most under-rated worker in US wrestling history.
The problem for me is just picking one worker. There are so many great workers from around the world past, present and future. Most people who watch wrestling got into it during the late 90's with the WWF Attitude period or in WCW the emergence of the NWO. It is a shame people have missed out on the outstanding stuff the the 1980's and stuff of today outside of the WWE.
One more thing, if you like wrestling check out CHIKARA. They are a smaller promotion based out of Philadelphia. The matches are great, the wrestlers have fun gimmicks and the promotion is for everyone in the family. They are one of the few things keeping me into wrestling.