My daughter has a '13 Jetta gasser which I drove extensively last week when visiting her in LA. I have a '12 Golf. Differences I'd note are:
- Jetta has a softer ride, although a Premium maybe less so with its larger wheels
- Golf has crisper handling
- Golf has better seats (and cloth, which I prefer)
- Golf has electric heater controls, where the latest Jetta went back to MKIV mechanical ones
- Jetta has a much larger rear seat area and a HUGE trunk
- I would have a hard time getting used to the lack of temperature gauge and the LED fuel gauge in the Jetta
- Golf is easier to park in the city (I was in Boston today and was reminded of how much that can matter)
- Some say the Golf has better headlights (can't verify this)
I'm not going to compare features or controls as neither of the cars I drive are the same as what you're considering: My Golf is option-free. And I don't think anyone can point to any significant differences in assembly quality between the two cars, with the possible exception of me reading here about more paint quality issues on the Jetta than the Golf. Jettas were criticized for interior rattles when they first came out, but now they seem better. If anything my daughter's Jetta has fewer rattles than the Golf, although the Golf's seem to come out in cold weather, which LA doesn't have.
If I had to do it again I would probably get another Golf, mostly because I prefer the versatility of the hatchback and I like the car's appearance better. But the Jetta isn't bad. And I have to admit I find the relative rarity of the Golf (especially the 2 door) appealing.