I am partial to the twilight shift because I could work another FT job and UPS PT. I worked preload (sunrise) for 8 years until I went driving, and that last year was a bitch. Always been a morning person until that last year.
As previously said, do what works best for you and your family. Twilight shift, you never have to worry about missing your favorite show, because you won't be watching them. Sunrise, get used to going to bed at 9 p.m. Twilight is easier on the body. We are normally awake and alert at that time of day after having 8 hours of normal sleep. Sunrise is easier to have a balanced life. You will at least have a couple of hours in the early evening do do things with fam and friends. But the hours sleeping will never be normal. Get used to 5-6hours daily and You will look at 6 a.m. on weekends as "sleeping in."
I think loading trucks in the A.M. is the hardest job of ALL jobs at UPS. And remember, if you are in it to get a job driving, it will most likely be a long wait, (but worth it) so take the job you think you will be able to tolerate for the next 8-10 years. (took me 8 years PT to drive at my small center. And the economy was booming then, so.....might be a while.) Hey, GOOD LUCK!!!! And I mean that sincerely. Not sarcastically. It's hard to start any new job. ( and now let's all repeat what we have been told oh so many times since 2008 "At least you have a job!"
And don't be put off by some of these people here. There are so many lurkers who won't comment because of what others may say. It's our loss that we never hear what they think. Kind of like the new "silent majority."