The 180/4 has a minimum focusing distance (object-front lens) of 1,3m, the 250/5,6 of 2,2m according to the datasheets.
The 180mm is also said to be well suited for macro work.
General guidance is with either the 150 or the 180, an 8mm or 16mm extension tube. It's enough to bump up the close focus without altering exposure significantly (you're talking 1/4 or 1/3 stop compensation, which your aperture/shutter combination isn't capable of anyway). If you think in terms of 35mm lenses, the difference between the 150 and 180 focal-length wise is the difference between an 85 and a 100. Frankly, I'd go for the 180 if you have to choose.
Keep in mind too that the 180 is physically somewhat longer and heavier than the 150. Depends what type of use you are planning to put it to, but for my purposes I wouldn't want a bigger heavier lens than the 150. You may feel differently, but just thought I'd mention it...
The 180 is longer, heavier and more expensive. It has a touch more distortion and vignetting. But yes, it is slightly sharper. It's that reason alone that people usually say "get the 180" and why it costs more. ;)
You'll almost certainly want to pick up the aforementioned 8/16mm extension tubes. You can then focus much closer; especially combined!