eqnarray or align?!
http://www.tug.org/TUGboat/tb33-1/tb103madsen.pdf
Whenever the eqnarray environment appears in a question or example of a problem on comp.text. tex, tex.stackexchange.com or other fora there is a high probability that someone will tell the poster not to use eqnarray. This article will provide some examples of why many of us consider eqnarray to be harmful and why it should not be used.
\enqarrayvs\align. – Joseph Wright♦ Dec 15 '12 at 17:48