class inheritance question

If I have a class

class something {}

and a subclass

class something::blah ($var=0) inherits something {
    class { 'something::aaa': somevar => 1, }
    class { 'something::bbb': somevar => 2, }
}

should the classes called from the subclass inherit the parent class? e.g. 
which is good practice?

class something::bbb($somevar) inherits something {}
or:
class something::bbb($somevar) {}

Also, what is the best way to set $somevar in something::bbb from a node 
definition?

Thanks.