some biased opinions here
coming from a 180sx owners perspective (please note I have driven a lot of 32 gts-ts, gtrs etc).
The sr20det is potent and cheap to mod, extract 200kw to 250kw easily depending on budget. it is reliable if u dont keep it at redline and maintain it well, although a lot have been thrashed. rb20dets are nice, smooth engines, great note but dont feel like they have the torque or the low-mid range punch the sr20 has.
The 180sx (with coilovers) handles a LOT better than any coilover equipped r32 I have ever driven. 32s just feel heavy and slow to turn in, the 180 is very responisve in its turn in, can enter corners MUCH faster etc etc etc. no bias here, just fact.
as for looks etc, thats all personal opinion, both can look great. interior wise, each to their own.
I truly believe the 180sx is a better car than the 32 (i dont like silvias)...but its all down to personal opinion. but i do say the 180 does handle better, can have the same power potential and is cheaper on the fuel.