Power
If you're working as a contractor, you'll have a lot of power to create your own schedule and choose who you'd like to work for. You choose when, where, and for whom you work...or don't work, if the job is crummy, the pay is low, or the boss is a total jerk. It's your call, and only that stack of unpaid bills can force you to take on a job that you don't want to do.
If you're employed by an institution, like a factory or a power plant, you'll have less power over the jobs you take on. On the other hand, you'll get a regular paycheck, which will make budgeting a lot easier. For some people, that's a great trade-off; others might find the loss of power to be a deal breaker.
Finally, and perhaps best of all, you'll be a master of machines. Tony Stark couldn't be Iron Man without knowing how to fine-tune a few engines, right? Okay, maybe you won't be Iron Man—but it's still pretty cool that you could do some maintenance on his suit.