Depends on what you want to do with it!
Many people hate the PA28-140's overhead trimmer, but once you get used to it, it can be easier than fumbling around between the seats of the -161. Personally I prefer the handling of the -140 but not the 'mph' ASI.
PA28-180 is quicker than the -140, but if your use that speed, it will drink fuel at an a Oliver Reed rate!
Given the choice (and the same avionics in each), I'd personally go for a nice -180 if one was available, preferably a PA28R-180 if the funds were available!