GTR will have the RB26DETT
GTS4 will have the RB20DET
one is a 2.6 liter the other is a 2.0. the 26 being a twin turbo and more displacement you'll have more fuel cost and more maintenance cost. and slightly more complicated. here's a post from another thread comparing the engines.
the awd function of the car is primitive. basically it just kicks in when your rear tires start to break loose. the GTR and GTS4 have different gearing in the trans.
either way you are going to spend good money on either car to drive it and keep it maintained. there are a lot of good articles out there that cover this.
here's my opinion. skip the RB20 engine, you'll get more HP from an SR20 for a quarter of the price. if you want a r32 skyline get a gtr, if you just want a skyline wait for the r33s get a gts. rb25s with big turbos produce good power. wait and save and get what you want, don't settle. don't use the car as daily driver, it's an import and old, things will break and you won't be able to buy everything at autozone. money to car ratio is off balance for the skyline, so much hype surrounds the car. in the end you are paying 20% more for a car just because it's a GTR or skyline. the car is a classic icon and i love having one in my garage, maybe two soon
I've owned a few skylines now, i love them, they converted me from american muscle to japanese turbo. i also advocate for japan-partner. but do your own homework on your state laws, good luck cali owners.