Ben,
From my observations, the suggestions you find out there are based on bro-science, a few clinicals, and product pamphlets. The pamphlets tell you to rotate sites, never apply to the scrotum, don't put on boney spots, etc, and is based mainly on minimizing skin irritation and potential blistering, not site efficiency. The bro-science is often better than you'd think with suggestions offering higher site efficiency, but it's nonetheless coming from somebody who isn't you! Therefore, all these different opinions and sources of information can be useful, but they have their limitations as it applies to individuals.
I won't recommend one site over another because it depends on many individual factors and takes some personal experimentation.
- How fast are you getting dressed after you apply?
- Will you be sweating a lot in that area?
- To what degree will your clothing be in contact with the application site?
- How many applications will you be using daily?
- Do you have any specific sensitive areas of skin?
- What are you trying to accomplish (are you going to the gym in 10 minutes or going on a date an hour from now?)
etc..
It should all be considered for maximum individual efficiency, but I doubt it really matters all that much in the end.
I like outer arms/shoulders, abdomen and inner forearms personally. Hot spots like the axilla are supposed to work faster, while open areas like forearms are significantly slower and more sustained.