I thought you asked '170tdi or tfsi or girlfriend' as the answer would definitely be TFSI!
The 170 is a terrible car for short journeys, it has a DPF and a diesel is not that economical on short trips (more than a petrol granted).
Guess it depends if she wants miles to the gallon, or smiles to the gallon?
Also, whereas the Leon shares many part numbers with the mk5, it has poor visibility and not that good an interior. Before anyone shoots me down I have an Altea and my bro in law has a mk2 Cupra.