I've owned a 180SX before, and own an S14 and R32 atm...
R32 is roomier on the inside, has better brakes, better suspension geometry and an engine that I'm more familiar with (owned about 4 R32's now). The interior trim is better than an S13 or 180sx. Availability of wheels in 5 stud is much better than in 4 stud. I don't see the point in buying a lower spec car and spending money upgrading it to be level with a higher spec car that costs around the same.
The S13 is an entry level sports car in the nissan lineup if you think about it. R32 GTSt's are a step up from that.
That said the body styling of a 180SX is kinda timeless... a simple facelift to an S15 front and it looks 10 years newer. An R32 unfortunately still looks like its stuck in the early 90's regardless of facelifts. S13 silvia's look like they're stuck in the 80's regardless of what you do to them.
I'd say an R32 GTSt and an S14 is about on par. The choice would be real hard, and I'd probably pick the S14 over the R32.