I would recommend the 5w-20 synthetic or the 0w-20 synthetic. Our local dealer recommended the 0w-20 for my TCH as we live in the hot desert. I asked their tech and he said they have had no problems using it in the prius and Camry's.

Your right, the old rule was the thicker the oil the better the film strength. That might be so with the older dino oils but with synthetics they have a very high film strength even if the oil is a 0w or 5w oil.

Dino oils have also improved a lot over the last 10 years. The additives they now use are much better. It's best to run a synthetic blend or even better stick to a 100% synthetic oil.