If this is your first car and want to keep costs low with decent performance then consider a 1.4 TSI 122ps or 1.9 TDI models. Both are in the low insurance bracket with enough grunt to get by day to day without feeling too strained. They should've depreciated low enough to become cheap to buy, look for at least the SE models for better specs (alloys, trip computer, front and rear speakers etc.).
Avoid the 1.4 (80/90ps) or 2.0 SDI as they are really slow and becomes hard work to get going. The uprated 1.4 TSI's (140/170) while peppy are quite problematic in the MK5's with some experiencing piston slaps and stretched chains so avoid these to save potential grief. I had a 1.6 FSI 115ps before my GTI and it was OK if not spectacular, they are pretty pricey to tax too considering the performance (£205 if I recall, the MK5 GTI is only £70 more with almost twice the power!).
2.0 TDI is a solid engine with punchy performance but as they are usually on the GT models so insurance might be out of reach if you're struggling now. Personally I would plump for a 1.9 TDI SE/Match if I was a first timer - torquey, good economy, cheap to run and can be remapped if you want a bit more pep.