The most important detail is whether or not a specific prop suits the engine on your airplane and pulls that airplane the way you want it.

Some composite props flex the least of any type props (that're legal). Some nylon ones flexed like rubber. The filled nylon ones (plastic by definition) don't flex much. You can answer the question yourself easily by dropping by a hobby shop. Make sure nobody is watching and flex 'em all. See which bends the most. If you can twist them with your hand, they're going to twist under flight loads.

In actual use flex doesn't mean much at all. The prop pulls through the manuevers you want or it doesn't.

Differences based on composition also don't hold up. Master Airscrew and APC are both filled plastic. But the APC tips are paper thin and can be twisted easily. The MA tips are usually still airfoiled and thick. Is it the plastic or the cross section that matters. So just the composition isn't the point.

The point of decision most often mentioned is that wood props don't stand up as well to landing bounces. So beginners are often told to get a plastic prop and "it'll last longer". It probably will.

BTW, back in the old days when Goodyear racers were homebuilt midget airplanes, one of them had a "home made" wooden prop. This is full scale, not models. And the airplane was a rocket (for the time). Seems the blade twisted under load and bent into more pitch on the straights and less in the turns. So twisting and flexing ain't automatically bad.