I have used both the Lee Handprimer and RCBS Handprimer.
IMO the RCBS is much more comfortable in the way it fits my hand and the ease with which it sits the primers.
I agree with Art that it was more comfortable to use both thumbs on the Lee, which in turns slows down the process for me.
The RCBS is more expensive but it does feel alot stronger than the Lee. However, my friend who owns the Lee has loaded thousands of rounds with no problems.
Me, I plan on buying another RCBS so I can have one for small primers and one for Large Primers, and another Lee Universal Shellholder set, so I have one set of shellholders for the primer and one set for the press.
Happy Priming