Personally, I've gone for the later, fatter version.
I used to like the original design, which is what she sported when we first became acquainted back in '73. As Chris says, it was sleek, unique and certainly in keeping with her modern lines. Moving on slightly, the only good thing to come of the pebble grey post Falklands colour scheme was the introduction of the traditional Cunard funnel colours, which in my opinion improved the overall look of the ship at that time (once the hull was repainted).
I didn't like the new, fatter version at the time yet looking back now at pictures from the early days, the original funnel doesn't look right. Maybe it's because I've become so used to seeing the later incarnation but irrespective which one we might prefer (and it's purely a matter of personal preference), it's still the best damn funnel around and unlikely to be surpassed IMHO.