Most any field of engineering is a pretty good gig, but if you are asking for what's the next big thing then it's biochemical engineering. Stupid high barrier to entry though, you can't just gobble something together and "trust me, I'm an engineer". In that field, you actually have to know what you are doing. It's more genuine scientific research than engineering as it is right now.

If you want a low barrier of entry, then industrial controls engineer. On the low end it barely counts as engineering, read the manual and push the buttons to configure ready made industrial hardware. And there is a lot of demand for it.