This is not a platform specific issue. Instead, you ask a question about development environments that come down to personal preference. Do you like working with emacs in general more than you like working with Eclipse? Do you prefer to "create your own environment from different scenarios and your own lisp hacking approach for a monolithic distribution-plus-plugins approach?
If you can be more productive with one or the other, what you should use. This has nothing to do with Android development and, say, writing web applications.
See the previous question: What are the effectiveness of Emacs or Vim vs Eclipse?
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