http://blog.bigbinary.com/2012/01/08/alias-vs-alias-method.html

This is because alias is a keyword and it is lexically scoped. It means it treats self as the value of self at the time the source code was read . In contrast alias_method treats self as the value determined at the run time.

Overall my recommendation would be to use alias_method. Since alias_method is a method defined in class Module it can be overridden later and it offers more flexibility