As an ATCO in the UK I think I would respond exactly the same whether you told me you'd had an engine failure, called PAN or called MAYDAY and you'd get the fire trucks in attendance if my rules say so regardless of whether you wanted them or not. Some issues like fuel or medical really require a PAN to gain any extra priority, but as human beings we'd do our best to help anyway. Squawking emergency does get attention - you may not think the controller receiving a MAYDAY call needs to see that on the radar too, but it also breaks through to adjacent sectors' radars (often filtered out), who will then do their best not to bother your controller or to clear the sky around you. Bottom line is still aviate, navigate, communicate and it's is far preferable to get down safely (as in BAW38) rather worry about niff-naff like correct radio call (as in BAW38).