tough choice. i just bought a 180sx and my mate picked up an R33 gtst for $13500. car has only done 75000kms on the clock. he got a pretty good bargain. (good thing about living in WA, all the overseas asian students but jap cars and sell them really cheap when they have to go home. 5 months later my mate sold the skyline for $20 000)
ive driven both cars and i find the skyline has better top end, then my 180. i used to beat the skyline in drags until my mate put a FMIC on and got it tuned. skyline chews more gas but it has a better interior and a lot more leg room than the 180. only a midget would be able to set in the back of the 180. the stock 180's look shit house. both engines are reliable and good for heaps of mods.
heres my 180.