The best software development methodology is no development methodology and the same goes with the best software development process. Going agile means embracing the fact that processes, methods and procedures are counter productive in small efficient teams. Small teams tend to value raw productivity, direct communication and using various approaches in hacking their way through. The efficiency of true agile teams cannot be reproduced by any formal process - as it is generally impossible to enforce the same dynamics in every approach to any possible problem.
You cannot shoehorn the true agile into a set of rules, procedures or even practices, because being agile means adopting individual approach to every problem given individual team capabilities. Original concepts behind agile manifesto canot not be covered by a rigid process, sometimes even requiring certification. Software development remains young enough discipline that in most part remains reminiscent of craftmanship more than engineering. No process would automatically allow optimisation of delivery of innovation or experimentation in order to scale small teams into larger ones. Most of attempts trying to make development teams larger and productive turn into optimising some aspects of productivity with no positive impact on delivery.
Agile approach to software development seems more popular than ever. Yet the agile name gets blurred through misunderstanding and usurpation. Positive effects of agile approach can be observed only in self guided small teams focused on delivery with minimum or no process to follow. Agile teams need to be small and coherent, with strong sense of security, yet open to experimentation. In fact the only way to remain true to the original ideas of agile is to build products out of lots of small programs by many small teams. When software is done right, it requires a fraction of the human resources to create and maintain. Changes are simple and rapid. Defects are few and far between. Effort is minimized, and functionality and flexibility are maximized.