For the average shooter the polymer trigger works fine. For those who put tens of thousands of rounds through their guns (competition), the metal trigger will last longer.
Most experienced shooters prefer a flatter trigger as it gives them the option of where to place their finger on the trigger. It gives them a better feel. This can help with trigger control and accuracy.
A curved trigger forces the shooter to place the finger in just one way--average for everyone. Curved triggers are especially helpful for hard trigger pulls, like 8+ pounds for a DAO or DA/SA trigger because it helps stabilize the trigger finger, usually inserted farther across the trigger to gain more pulling power. Neither of these considerations should apply to a striker fired or SA gun.
It's always good to try before you buy. You can dry fire different guns with different triggers from your local gun store case. Some people prefer a curved trigger just because most guns have them.
The classic 1911 design has a flat trigger that many shooters love with its straight pull to the rear.