Objective-C: Checking class type, is it better to use isKindOfClass or is ToSelector responding?

It is more appropriate to check the type of the class by calling isKindOfClass :, or use the duck print approach by simply checking to see if it supports the method you are looking for through responseSoSelector :?

Here the code I think of is written in two ways:

for (id widget in self.widgets)
{
    [self tryToRefresh:widget];

    // Does this widget have sources? Refresh them, too.
    if ([widget isKindOfClass:[WidgetWithSources class]])
    {
        for (Source* source in [widget sources])
        {
            [self tryToRefresh:source];
        }
    }
}

As an alternative:

for (id widget in self.widgets)
{
    [self tryToRefresh:widget];

    // Does this widget have sources? Refresh them, too.
    if ([widget respondsToSelector:(@selector(sources))])
    {
        for (Source* source in [widget sources])
        {
            [self tryToRefresh:source];
        }
    }
}