I'd expect that the 1.4 16V engine will not be Euro6 compliant, so they can not be sold new after 1st September - that is my understanding of these engines and others.
If that is true, the road tax will start to be ramped up year on year on older engines, that would make buying the 1.2TSI the better buy.
Having said that, I'd expect these 1.2TSI engines to disappear as well with the introduction of the cleaner and probably cheaper to build 1.0TSI engines.
For all that, I have just bought my wife a new Polo 1.2TSI 110PS and was keen to "grab" one of the last ones built as I don't know what the 1.0TSI engines will turn out to be as far as reliability/durability is concerned.
Wife's previous car was a 2002 Polo 1.4 16V 75PS which is a close relation of the latest 1.4 16V 85PS, these engines are not "exciting" but do seem to be reliable, I'd doubt if my wife will get 13 years use out of her new 1.2TSI engine, so many ancillaries and sensors to worry about, but you can't stop progress. Don't get me wrong, given the choice of the 1.4 85PS and 1.2TSI 110PS, I'm sure that she would rather having the 1.2TSI 110PS.
Really depends what you want and expect from your new car.