I live on both sides of that fence. I have been a ham radio operator for over 35 years and I am also a controls engineer. In many ways, RF engineering is simpler because it primarily concerns itself with steady state calculations. The differential math is simpler. In controls engineering, we're often concerned about minimizing the settling time on a loop. Tuning feedback loops is important.
Controls Engineering is a very broad and deep field. You'll find yourself working with fluid mechanics, thermodynamics, and electronics all at once. Human factors also figure into the design. Your designs may have to be used by people who are not in the best mental health. They may be fatigued, under extreme stress, or simply ignorant. You have to think of usability considerations.
In RF engineering, however, the systems designs are interesting and challenging. Working on a high speed modems for something that will need to work at hundreds of megabits per second is a real challenge. Designing a better system to replace Bluetooth is also interesting.
However, over the long haul, there are likely to be more industrial automation jobs out there than radio jobs. Most of the radio systems are being designed by software jockeys with lots of models and tweaks. There is certainly room in the PCS cellular business for more engineers, but you might not like the kind of work you may get.
Industrial automation jobs can be very secure and stable, or they be one contract after another all over the world. You'll have to learn a lot about all sorts of industrial processes and regulations. I chose controls engineering, and I can honestly say after 25 years, that I'd recommend this field highly to any up and coming engineer. There will be many opportunities, many challenges, and lots of interesting work.
But, whatever you choose, I wish you the best of good fortune, and enjoy!