Hi Gromit60, and welcome.
At the risk of starting yet another editor war, they are different editors and they each have their own strengths and weaknesses. I use both, depending on what I’m doing.
Best to try each of them out and decide which features you like. IMHO (and this is not a fact!) Potlatch is more advanced than it first appears and JOSM is less complicated than it first appears!
Steve