Having an animal sleep the entire way through the trip is by far the easiest for them.
-Ken
Sedating your animal is so unsafe. Here is an article from the American Veterinary Medical Association.
http://www.avma.org/careforanimals/animatedjourneys/livingwithpets/sedate.asp
My dog has flown 6 or 7 times and has never had a problem in the cargo hold. No long term problems except for an amazingly long pee when we let him out of his kennel after landing.