simple but confused (oil)

I am trying to change the oil on my wife's 2005 impala. The book and car say to use a 5W-30, but I called the dealership and they said use 5 or 10w-40. So what should I use? I do not want to put the wrong stuff in a mess up my warranty.

30 weight. you can either do 5w-30 or 10w-30 depending on the weahter, NOT 40 weight.

5w-30

if you got the cash go synthetic