both provide a find-method functionality (and rubyamp a lot more).
i am not very familiar with rubyamp, but looking at the code i see the
uses the “selected word” / “cursor position” to lookup the method
definition by pressing “^-”
prompts you for a “methodname” to search for
imho is pressing “^-” much simpler than entering a complete methodname
to search for.
finddef will find method definitions in the open project, rubygems and
in an usersupplied searchpath if you wish - i have not used rubyamp,
so i do not know if this is a difference between the two.