It largely depends on how you cook.
I have a disc (plow disc with handles) and a griddle.
For fajitas or stir fry the disk is perfect. The disc deal was out of necessity since I was cooking fajitas for 100 folks and it was the fastest way to do it in that scenario. I didn't have the griddle at the time.
The more multi task of the two is the griddle. Any thing like burgers or hotdogs or such I'm choosing the griddle every time!
The disc is a great choice for large quantities of breakfast tacos though. I've used it more than anything for that. Specifically youth baseball/football/robotics/whatever my kiddos are doing at the time.