I'd say plumbing. The only the that separates a house from a barn is plumbing. We're the first and last on the job site. The plumbing has to be EXACT before the rest of the bldg goes up. A beautiful bathroom/kitchen is usually the final decision for home buyers.
After that hvac because the industry is advancing technology wise so fast that most guys over 40 can't keep up. Nowadays if you're not tech savvy, you can't work on the equipment. Hvac tools cost a fukkin grip tho
Hepatitis?

Never known a good plumber to catch ANYof these diseases. There's not one job in plumbing where ur skin touches waste. You gotta be one serious jack leg mechanic to put your life in danger of that shyt. There's a tool for EVERYTHING.
Side note- most plumbers build up an abnormally strong immune system because we work with specific metals (copper, iron, lead). People say all kinds of crazy shyt bc they think we unclog shytty toilets all day

Truthfully, that myth works to our advantage.
Firefighting is cool with me. Probably has its advantages over a trade but ull be working for the city