The profession exam is purely about engineering law and ethics.
I thought the average pay for Mech was higher than Civil. I don't think Civil is very creative. It's mostly about verifying conformance to existing building standards. Also, I think the unemployment rate is quite high in that field.Due to the pay of mechanical engineers and job market, I'd probably take civil.
If you're more interested in the topic rather than the money, I would recommend electrical. The work is much more creative than civil or mechanical. I'm formerly a mech. I quickly got tired of it. The job involves mostly project management, fitting parts together and lots of drafting (CAD). The stuff you learn in mech courses really isn't useful for hobby projects.
I learned electronics and software on my own and eventually changed fields. I like it much better. It involve much more creative design, troubleshooting and constant learning.
Hopefully I don't offend any Mech's or Civils. It's just an opinion based on personal experience.
If you like building things, get a mini-lathe and mill and convert it to CNC! That's what I'm doing, when I have time. The combo will allow you to create almost any other machines you can think of.Plus, I want to build things, and developments sounds like more fun, although most of my projects that I'd like to work on would be more EE or ME.
I don't know what your current degree is in. If it's IT, you might be able to switch over to embedded programming within the company. This will get you into a position where you can quickly learn electronics without going back to school. The topic really isn't that difficult to learn on your own if you're motivated. I didn't even have to take any night courses.