Ok, time for some stats related to the actual thread question. Leaving batting completely out of it, because there is nothing about batting in the original thread and poll question, I've compiled these stats.
Mitchell Johnson - 22 tests
99 wickets @ 27.91 - 2 5 wicket hauls
James Anderson - 38 tests
130 wickets @ 34.23 - 6 5 wicket hauls
On average Anderson takes 3.4 wickets per game, whilst he is becoming the spearhead, he has to contend with Flintoff and Harmison dominating proceedings whilst they are in the team.
Johnson on the other hand, is the spearhead now, with Lee injured, Siddle and Johnson will share the spearhead role in the future, but at the moment, it's Johnsons job. He takes 4.5 wickets per game, and averages much better too.
Lets take it back to another closer comparison, after 22 tests.
Mitchell Johnson - 22 tests
99 wickets @ 27.91 - 2 5 wicket hauls
James Anderson - 22 tests
70 wickets @ 38.77 - 4 5 wicket hauls
So Anderson has kicked on and improved as a bowler from his 22nd test to his 38th, not only is that my opinion but the statistics show this as well.
At the moment, Anderson has a strike rate of 59.2, not quite as good as Johnson's 56.3. Johnson also trumps Anderson with a better economy, Anderson's 3.46 doesn't compete with Johnson's 2.97.
So, I think we can safely say, that Johnson has performed better with the ball, and a better bowling average, more wickets per match, better strike rate, and a better economy rate. Whether he is the better bowler or not, is debatable, because both are fantastic bowlers when they swing the ball, but with Johnson isn't is a regularity. I look forward to having this discussion again when they end their career.