Better have an idea what exceptions you need to throw later.
There's the so called Liskov substitution principle, which recommends not to throw exceptions in subclasses that would not be thrown by the super class.
Liskov substitution principle aka. design by contract:
http://en.wikipedia.org/wiki/Liskov_substitution_principle
If you are uncertain which Exception need to be thrown, use "throws Exception" (even if it is uncool). Just do not allow unexpected behaviour by implementing classes when they throw exceptions where they weren't planned by you.
The worst case would be a programmer who desperately throws runtime exceptions because of a lack of throws-declarations.
