I agree with Neil you will be able to pick off some lovely candid shots with the 70-300. Having said that the fifty is a great portrait lens and would be faster in low light situations during the service and doesn't take up too much pocket space.
Enjoy.
I've been to a few weddings with similar lenses. My advice would be to stand back and use the 70-300 to capture some candid pictures. I did this exclusively at a friends wedding in August last year and found the bride and groom really liked how natural people looked. They've even used some of them around their house favouring them to the posed pictures.
It's great experience and you'll capture some unique momoents
1.2f said:hi nikki, hope you don't mind me jumping in on your post however, i am also taking some phots at a friends wedding next week and was wondering which lens i should take with me. i am still in the process of deciding whether to buy a 17-55 or 24-70 to compliment my lens line-up however, if the purchase is made prior to the wedding then this lens will also be a contender to use on the day.