Round rackets
Weight sits low, near your hand. The racket swings quickly, the sweet spot is the biggest of the three shapes, and a ball hit off the edge still goes where you aimed.
You give up top-end power. A round frame will not end a point with one smash the way a diamond does. What it gives back is that almost nothing you hit turns into a free point for the other team.
Buy a round if you are in your first two seasons, or if your game is built on keeping the ball in play and winning from the back.