Why do you love Mechanical Engineering or Aerospace Engineering?

I studied both mechanical and aerospace engineering with a focus on space hardware. I always wanted to work on robots for space and Mars. I went to RPI for undergrad (aero/mechE), U. Maryland for MS while working (aerospace, focusing on space hardware), and CMU for MS (robotics). I found I loved hardware design engineering. I designed stuff for Mars (at JPL NASA) and astronauts (for NASA via Swales/ATK), and now do R&D in biomedical.

Cool stuff that I like about my job:
I get to invent stuff that's never been made before, or at least exactly that way.
I've gotten to work with really brilliant people, who are fun to work and chat with.
While ideas don't always get used, I get to brainstorm some really wacky stuff.
You get to play with and learn about all kinds of new materials and technologies. You're constantly learning.
I get to tinker and build with my hands. I love building stuff, and find it relaxing.
Things you learn in one industry often surprisingly transfer to other industries.
New problems all the time.
I get to solve fun math problems that relate to real life...usually.
* I now have an engineering mindset that drives me to solving all kind of the world's problems, with a structured problem solving method (identifying the problem, finding goals, establishing a plan...). Ok, sometimes this backfires at 3am, but otherwise, you'll never run a potluck the same way again.

Why I recommend a mechE (and/or Aero degree):
Once you get the foundations (theoretical math) of mechanical engineering, you'll be able to decipher pretty much anything new. This is powerful (and makes you highly employable). If you don't choose engineering for a career, you'll still have great thinking skills.
Nearly guaranteed income when you get out of school. Starting salaries in CA are ~$60k.
* You will develop amazing project management skills (after experience working on a design project).

Unsolicited career advice:
Make sure your university has a legit co-op/internship program with engineering companies you want to work for. Work experience is how you'll figure out if you really like working in engineering/aerospace. I co-oped at JPL and fell in love with the work.
Many (but not all) aerospace jobs in the US require a security clearance. See if you are eligible.

Go to a school that has options outside of aerospace if you decide that the theory is too much (or go to a school that has a really good hands-on approach). Finding the right major is a compromise between your long term dreams and what makes you happy now.
When looking for jobs in aerospace, consider the company and its culture very carefully. The aerospace industry is notoriously culturally behind the rest of the industry, and can be a really aggressive work environment. Do your company research before you pick one.
Don't get stuck doing paperwork if you want to build things. A lot of big-aerospace and NASA work requires lots of paperwork and paper engineering. If you want to do hardware, you'll have to find a hardware position (which means focusing more on your mechanical engineering skills). Systems engineering, project management, quality, mission assurance all involve paper and not a lot of physical hardware. Orbit/trajectory planning involves some cool simulation work and some paperwork (this would be more on the aero side of things).
Never pay for a graduate degree. If you're any good, it's free. You'll either get a stipend from a graduate program, or your company should pay for tuition reimbursement.
* You don't need a graduate degree for most positions. Exceptions being controls and some trajectory planing fields.

Best of luck.

I suppose you know the sayings:
1) There are TWO sides to a COIN,
2) There are many ways to SKIN a poor CAT.
So, here are your NEGATIVE comment(s), as someone with BS & MS in ME, plus MBA & P.E.
1. Go FIRST for money, not after your dreams, as I did (40) years ago.
2. Mech Engineers are at the bottom of "totem pole" under Petroleum, PROCESS, Electrical, Instrument guys.
3. Last week, a top recruiter AEROTEK advertised for ME in Orlando, for a tragic $17/hour = $35,000 a year.
4. My own wife is a Doctor (MD), her own NURSES (RN & LVN) make $35/hour = $70,000 ++++
5. Aerospace is for BIRDS, if God wanted us to go to moon, we woulda have wings :))))
6. Go for finance, law, medical...
7. If you have to be an engineer, read item #2 above.
8. Good luck, to all my engineer friends.. from "forced-retired by $40/barrel oil" Andre

I studied Mechanical Engineering at Vanderbilt University and specialized in aerospace my senior year. I started working for a company called Pratt and Whitney developing jet engines directly out of school. I no longer work for them so I can give a candid response but I should mention that this was my experience and it will differ from person to person.

Let's start with the positives. Most large aerospace companies are hiring a lot these days. The age of most engineers is at or above the expected retirement age so there are a lot of opportunities. In addition, you will most likely be hired with a number of people your same age which is important from a social work experience standpoint. Just like the previous individual, I too had the experience of working with a lot of new technology and was able to garner a number of patents during my time which I still find very exciting.

Now onto the negatives. Quoting the previous post "While ideas don't always get used, I get to brainstorm some really wacky stuff". This is true and, long term, can be quite frustrating. You have the opportunity to think about interesting solutions to complex problems, but rarely do you get to implement them. In addition, product cycles tend to be on the 15-20 year time period so, unless you work at the same company for your whole life, you probably won't see one of your projects go from an idea to a tangible product. In addition, most large aerospace companies are extremely hierarchical so don't expect you ideas to be taken seriously right off the bat. All it takes is one guy above you saying no and your whole program will shut down. Oh, and the government funding aspect is a big bummer and is not very dependable either. Lastly, if you end up in an operational role, you will pretty much be plugging numbers into standard work that was developed 30 years ago to solve all your problems so there might not be much room for real "innovation".

My advice mirrors that of the previous poster. Find a University that offers Co-Op programs. Determine if Aerospace is really where you want to be for yourself. I have many friends who love the industry and have been in it for a number of years. I have others who don't so it is really all up to you. Also, I would recommend sticking to a broader ME degree. You don't want to pigeon hole yourself right out of school because you will change your mind a lot those first couple years in the working world.

My last nugget... Start something of your own in college. You will never have the time and resources that are available to you in school and technology has never been more DIY friendly.

Good Luck.