You don't say what the desired mission is and there are HUGE differences in capabilities between the two.
I have owned (1) 170 and (2) 180s. The best illustration I can give you is my "Tale of Two Airplanes".
I now have 4 kids, but at the time of my first story, I had one kid and a wife who thinks traveling and "truck size luggage" are synonymous. So we traveled to Colorado from Albuquerque over the pint sized 12,000 foot rocks you find running all through Colorado (dodged the larger 14,000 foot ones). I was and still am based at E98, 4,800 feet and 3,500 foot runway. The 170 was a 48 straight 170 with the stock 145hp in it (fresh, strong engine). In an effort to be proactive and limit my close horse wife to a manageable luggage level, I explained to her that she would be limited to one suitcase. To which she indicated would be no problem. Day of travel arrived and she was true to her word. There was only one suitcase. However, an Olympic weight lifter who can clean jerk 300 lbs couldn't have lifted that suitcase. When you added full fuel, stroller, portable crib, car seat, etc... we were definitely at gross (of course I would never fly over gross).
A quarter mile north of my strip is a line of trees about 40 to 50 feet high and I had to dodge them to clear the trees. My wife calmly asked if it was normal to be at tree level and I explained to her that I really wanted to provide the best view possibly for her and the little one and to not mind the sweat beading on my forehead.
We mushed along for another 30 miles and finally caught thermals and burned gas so that by the time I got to the Rocky Mtns, I had enough clearance to get over (barely), but there was definitely a period of time when I was wondering if I was going to have to return to base and load up the vehicle and use the travel mode of mere mortals.
Fast forward 10 years, I now have 3 mean, trouble making boys and decide to fly 2 of them and myself to Oshkosh and do the camping thing (although what possessed me to put my two trouble making boys in close proximity with millions of dollars of airplanes still escapes me). The phrase "get the hell away from that" was uttered more than a few times that weekend. I have extended baggage in my current bird and the BAS stowable seats. There was not an ounce of free space in that plane. With the monster Coleman family tent I tote around, the two coolers full of beer, soda and food, clothes, portable seats, etc. we were loaded to the gills and right at gross (of course I would never fly over gross). I left the same (E98) 3,500 foot strip at 4,800 feet elevation and the plane sprang off the ground. Immediately to the east (about 35 miles away) of the strip is a 10,000 foot mountain and we climbed straight over it. The airplane was just a sheer pleasure to travel in and there was no comparison to the old 170 days. The old adage of "if you can get it in the 180, you can lift it is pretty true.
I know the 180s are a level more expensive than the 170 but your capability will be so much more.
I am assuming that if you are on this website, you are probably into backcountry flying. If so, the 180 is just a much more capable bird.
If you can afford it, go the 180 route. You won't regret it. One of the best all around airplanes ever built.
Whatever transpires, good luck!! Larry