PAL uses 50 Hz, NTSC 60 Hz vertical refresh - so NTSC means less flicker.
This isn't quite as true as you make out. Certainly the time periods involved would mean PAL was more "flickery". However, PAL has a better resolution so the size of the flicker is less.
As the perception of vision varies from person to person some people notice the flicker in PAL more, they are more perceptive to time interval, and some people notice the flicker size in NTSC more, they are more perceptive to the flicker size.
Overall the quality of the connection tends to be way more important. Composite is quite frankly a steaming pile of plop, avoid it at all costs.
It also matters of course, the nature of whatever you are viewing. A Workbench screen is generated by the Amiga directly. If one was talking about a video the matter of source material, standards conversion, drop frames and all make the issue far more complex, but I'm not going to go into that right now, I'm far too busy today.
Sadly, in my experience, most of the video industry (I worked for many years as a DVD author for Touchstone productions) have less technical knowledge than they should have. Take out a DVD and check out some still menus, you will find many that flicker like mad, the sub-pic (selection highlight) in particular. This is easily improved by applying a single pixel vertical blur to the menu and sup-pic. Or better still by avoiding odd numbers of vertical pixels to any horizontal lines in the menu design. Not difficult but seldom done, sadly.
And all that's before we even consider the screen itself of course.
