In terms of Lean vs. Six Sigma, only time will tell.  Although there exists natural points of intersection, there are also points of incompatibility – philosophically and pragmatically speaking.  I would strongly suggest that you conduct a literature review into the stated issue so as to properly scale the scope and depth of an answer.  This will provide you with a deeper and richer understanding of the contrasts.  Please recognize that answers (related to this forum) are each constrained to 3500 characters.  To do any type of justice to your question, far more space would be required.

To facilitate a literature review, you should consider developing a simple spreadsheet with three columns.  The first column would define the row variable and be label as “Best Practice.”  For example, “using performance metrics to guide business operations.”  Another practice could be “using statistically designed experiments to isolate leverage variables in the process.”  Of course, the second column would be titled “Six Sigma,” and the third column would be called “Lean.”  Naturally, the cells of such a matrix would be used to record your summary commentary.  Of course, the source of each entry could also be provided.  As should be apparent, such a contribution would be “value added” to the many people that frequent the iSixSigma.com website.