I just recently picked up the 183, off eBay. While I love my 180 for liquid foundation, I love my 183 for mineral powder foundation (Bare Escentuals).
For rapid buffing, I find the short handle of the 183, easier. The heads are very similar in size and density. If I had to say one was denser, I would say the 183, but that might just be b/c mine's newer than my 180. I mostly wanted to pick up the 183 b/c A) I like a shorter handle for mineral foundation and B) I didn't want to use the 180 for liquid AND mineral.
HTH!