I enjoyed building my pond myself. It's a wonderful creative outlet for me. I enjoyed making the choices for it myself, and the satisfaction of knowing that (with a little help from my boyfriend) every rock is where I personally placed it.
Even professional companies don't necessarily make good decisions (after all, you've had problems with your current pond since the beginning). I figure if I am going to have issues with my pond, it will be easier to diagnose them if I know everything about the pond because I built it. I know the places it is most likely to leak or overflow. I know where plants have a lot of room for the root system in the waterfall because I know how much gravel had to be used to fill in the gaps.
My pond has flaws--places where the liner shows, for example. Those kind of flaws happen even with a contractor, and it's a lot easier to explain to visitors that my pond has flaws because I built it myself. The "flaws" stop being flaws and turn into charming home-made flair.
My pond is a constant work in progress. Because I built it and know exactly how it's set up, I can make dramatic changes that I wouldn't dare to do on a professionally built pond. It's not so "rigid" and "fixed."
My pond building skills have improved with practice. My first couple of ponds were not very good, and I already know ways I would improve my newest one if I had the time and money to start over. That is both a positive and negative of building your own pond. It is a steep learning curve and you are bound to make mistakes. However, I believe that you're just as likely to make something as good as what a contractor could make with just a little education and practice--and over time can probably go well beyond what most contractors could do.
But then, that's just me. To be fair, I've never had the money to sink on a contractor, so I am only going off of what I've seen others post online of their own experiences. I could be massively underestimating the quality of contractor work. For me, though, I don't have the budget to get a contractor's help every time my pond has issues. I'd have to fix any problems myself anytime something went wrong, so I'd rather know exactly what's going on with the pond.
Plus, I just really really love doing it. I can't say you'll feel the same way, but if you enjoy creative projects (crochet, painting, whatever) you'll probably find it extremely rewarding.