Welcome!
I was sort of in your boat. Mk4 R32 or Mk5 GTi?
As mpg was a big concern (of the Mrs, not me) I went for the GTi. I came in from a Mk4 V6 4Motion, which was pretty juicy, and the R32 is worse still. But take a look at a mint 3 dr Mk4 R32 in black or blue, and it's pretty hard to walk away!
The Mk5 GTi is without doubt the best car I've owned, it's a brilliant drive, but I do miss 4wd. In our climate, the ability to get the power down and have superb grip and traction in all weathers is such a bonus.
But on a dry day, the GTi is so much fun, I am literally beaming from ear to ear EVERY time I drive it, and it looks superb with Monza 2 alloys. I didn't want to spend more than 7 or 8 grand on this car, so it was easily the best car for my budget.
However, my next car will have the best of both worlds: 2.0 TFSI & 4WD.