What is the cleanest way to write this if..then logic

if (!String.IsNullOrEmpty(returnUrl))
{
    return Redirect(returnUrl);
}
return RedirectToAction("Open", "ServiceCall");

if (!String.IsNullOrEmpty(returnUrl))
{
   return Redirect(returnUrl);
}
else
{
    return RedirectToAction("Open", "ServiceCall");
}

return String.IsNullOrEmpty(returnUrl) ?
			RedirectToAction("Open", "ServiceCall") :
			Redirect(returnUrl);

return String.IsNullOrEmpty(returnUrl)
			? RedirectToAction("Open", "ServiceCall")
			: Redirect(returnUrl);

if (String.IsNullOrEmpty(returnUrl))
{
   return RedirectToAction("Open", "ServiceCall");
}
else
{
    return Redirect(returnUrl);
}

// Andrew Rollings solution
return String.IsNullOrEmpty(returnUrl) ?
                    RedirectToAction("Open", "ServiceCall") :
                    Redirect(returnUrl);

if (String.IsNullOrEmpty(returnUrl))
{
    return RedirectToAction("Open", "ServiceCall");
}
return Redirect(returnUrl);

if (!String.IsNullOrEmpty(returnUrl))
{
   result = Redirect(returnUrl);
}
else
{
    result = RedirectToAction("Open", "ServiceCall");
}

return result;

void myfunc()
{
    if (!String.IsNullOrEmpty(returnUrl))
    {
        return Redirect(returnUrl);
    }
    else
    {
        return RedirectToAction("Open", "ServiceCall");
    }
}

void myfunc()
{
    // ... maybe some code here ...

    if(!String.IsNullOrEmpty(returnUrl))
    {
       return Redirect(returnUrl);
    }

    // ... a bunch of other code ...

    return RedirectToAction("Open", "ServiceCall");
}

if (!String.IsNullOrEmpty(returnUrl))
    return Redirect(returnUrl);
else
    return RedirectToAction("Open", "ServiceCall");

return
  string.isNullorEmpty(returnUrl) ?
     RedirectToAction("Open", "ServiceCall") :
     Redirect(returnUrl);

if ( )
{
    return ...
}
return

if ( )
{
}
else
{
}

if ()
{
    code ...
}
else
{
    code...
}

if ( ) {
    code ...
} else {
   code ...
}

if(String.IsNullOrEmpty(returnUrl)) {
  return RedirectToAction("Open", "ServiceCall");
}
else{ return Redirect(returnUrl); }

if (!String.IsNullOrEmpty(returnUrl))
{
  // hooray, we have a URL
  return Redirect(returnUrl);
}
else
{
  // no url, go to the default place
  return RedirectToAction("Open", "ServiceCall");
}

if (!String.IsNullOrEmpty(returnUrl))
    return Redirect(returnUrl);
return RedirectToAction("Open", "ServiceCall");