I think that is a hard question to answer. The most fair way would probably be to run the two through a myriad of tests and see who came out on top.
Ideas for tests would be individual tests such as 40, vertical, bench press, etc. The ability to do many of these well, however, does not automatically convert to prowess in a particular sport.
Other ideas would be to have them perform different sports tests, such as kicking field goals, throwing a football, pitching a baseball, playing 18 holes of golf, etc.
I think it would be hard to deny that a top level professional soccer player is incredibly athletic, such as Messi who is fast, agile, and obviously has tremendous coordination and control of a ball. LeBron James would be strong, powerful, have great jumping ability, and obviously a clinical shooter of a basketball. Interesting thought though either way.
Tony Stewart is so much a better athlete than Henry! 
