I use both Navicat and pgAdmin3 these days.
One thing I like about pgAdmin3 is the ability to only execute the query you have highlighted and also the scratchpad. It's nice for exploratory querying. In Navicat, I like switching between various tabs where pgAdmin3 makes me switch between windows.
Both have some hilarious idiosyncrasies. When one locks up for no reason, I generally just alt-tab to the other.
Recently I was using pgAdmin3 and set my production database color to red. I happened to notice that the color didn't repaint back to green when I switched to my dev database. And Navicat seems to consistently hang whenever the network dies or burps mid-action, requiring a command-line kill.
Idiosyncrasies. :)