Wanda Krack wrote:
Either of the lenses should work well. If the weather is cloudy and overcast or rainy, I would suggest you use the l.8 lens as you wouldn't have to increase the ISO for the light. But, if it's sunny, and you find a shady spot to shoot, either should work well. You will want to move your body to increase and decrease the size of the folks in the frame with the prime lens tho and don't have to do that with the zoom. Have a good shoot!!
I vote for cloudy and/or bright/open shade. Along with that use your flash as fill flash. I probably use my flash outdoors more than indoors.
If you must shoot in the sun have them face away from the sun and use fill flash.
It is always nice to get shoots during the magic/golden hour (within the first of sunrise or the last hour before sunset).