Best DX camera vs cheapest FX body

Should I buy the best DX or the cheapest FX eg Nikon D7100 vs Nikon D610

Current approx prices in New Zealand for the D7100 is NZ$1500 & D610 is $2500.

Most extremists have their heart set on one or the other.
I'll simplify the decision making for you here in under a minute.

Its a simple answer based on 3 simple questions.

Is the shallower DOF you get on FX so very important to you that you would pay a whole thousand dollars just to have that??

Is the minor improvement in high ISO performance on FX so important to you that you'd pay a whole thousand for it??

Are you ok with the fact that the D7100 has more AF points at 51 scattered all thourhgout the frame whereas the D610 only has 39 packed mostly in the center, & you are still going to have to pay $1000 extra for a D600 to get the shallower DOF & the better ISO performance?

If yes, go for the D600!

If not, go with the D7100.

Both cameras are brilliant.

What if I can get a second hand D600 for close to the price of a new D7100?

Ok, that makes things easier on the wallet, but the questions don't change too much.
Do you care so much about superb shallow dof performance & slightly better ISo performance that you are ok to sacrifise getting more AF points of the D7100 in return for the D600?
If yes, yay for D600, if not yay for D7100

In reality, I wouldn't even buy a D7100, Id still buy a D7000, save the money & use it for better lenses. remember, no substitute for better lenses. Regardless of DX FX DSLR or any other photographic format on earth.

If I have a budget of $2000, should I buy a D600 & attach a 18-55mm VR kit lens, or a D7100 with a bunch of lenses?

Never forget the golden rule, lens before cameras. Optics before electronics.
Cameras are called electronic devices today, but they are not, they are optical devices.
Crappy optics = crappy photos, never forget that fact.
So forget the fancy body, get the fancy lens. You will not regret the decision & your work will outperform whats produced with cheapo lens on the fancy body.

I already have 3 lenses, but my photos are still not so good, what should I upgrade to?

Upgrade to reading more articles to improve your techniques. Then buy more lenses to try different forms of photography that you find intriguing. Then upgrade the lenses you have to the best in their class based on the ones you use the most. Then read more & upgrade your skills again. And then when thats done, upgrade your camera.
And if switching from DX to FX at that point, please dont forget to buy good FX lenses if you dont already have them.