I've got a 140TDI and was given a 1.4T whilst mine was in for a service. I couldn't believe the difference. Like chalk & cheese.
Don't get me wrong, I'm sure there are a lot of people quite happy with their 1.4Ts, just like I was very happy with our old 1.0 Yaris, but the 1.4 just hasn't got the torque - the low down push you get from the TDI.
The 1.4T would certainly be cheaper on tyres - because you'd never give it a bit too much gas and spin the tyres in the dry like I do accidentally but regularly in the TDI....
Its down to what you want from the car - but whatever you do, if you're really thinking of choosing between the two, make sure you test drive both to make an informed decision.
I would equate the 1.4T to our 1.3 Yaris SR. Its a lovely smooth petrol engine that you appreciate for its smoothness and refinement, but its never going to put a grin on your face through its power or torque delivery like the TDI can....
I go out in our Yaris and enjopy and appreciate its engine after the roughness of my Audi TDi, but they are two different types of engine and I appreciate having one of each type...