many years ago I used to be a rep for Hercules Chemical among other lines. My favorite dope is Real-Tuff but some guys liked Megaloc too. Rectorseal is also popular but it is a petro based dope as opposed to Teflon and as such should not be sued on plastic threads.
One trick many pipe fitters use and employ is to wrap the fitting with Teflon tape then apply the pipe dope. The quality of thread cuts is fairly poor these days so the combo of tape and dope works well. If you want to use one or the other definitely use dope over tape..