I would go the R34 GTT... you could get a good one for around 18K and you'll have enough left over for insurance with your budget.
I agree with Marc, a R33 GTR could be a little more tired, more maintenance etc... to me it's more of a car you get if you have good mechanical knowledge and have the time, money and space (garaging!) to baby it. It's not what I would get as a uni student, especially if you're going to be driving it there as a daily driver.
Resale value? It doesn't matter which one you get... it won't be pretty so I wouldn't be getting a Skyline if that's important to you
Standard or modified is entirely up to you. I just bought a GTT and I wanted a stock one as I didn't want one that someone else had messed around with too much. I ended up with a few minor mods that were a bonus but the car was clean and unmolested. I don't have the money to be putting it in a workshop if other people's "mods" get issues, and I don't have the knowledge to fix it myself.
Good luck and welcome to the forum Toni