Large Format ? Medium Format ? 35 mm ? Digital ?
For large groups or very large prints we use a large format camera with a negative size of 4X5 inches. For the important shots or large prints we use medium format camera with a negative size of 21/4 inches square. For the casual shots of say weddings guests or action shots we use 35 mm cameras.
A 35mm film negative has the resolution of a 30 mega-pixel digital camera. On the same professional 35 mm camera a digital back currently has between 5 or 6 mega-pixel resolution. So the film has 5 times the resolution of the digital. This translates in to a much higher quality print.
We like to use film for the original shot and scan it into digital with much higher resolution than available from a digital camera. This way you can have the best of both worlds.
Here is a photo of 4X5" film next to a strip of 35mm negatives followed by medium format film. All the sizes are the exact same material, you can see why a larger format gives a higher quality print.