Now; I'd say both. Back before the 1950s; I'd say "Them".
Since Roswell had taken place back in 1947, for a good fifteen to twenty years it would be easy to assume it was "Them". But now, you have to wonder if at least a quarter, to maybe even half of the proclaimed UFO sightings are probably "Us". It would probably take us a good decade or two to successfully back-engineer one of their crashed ships. And then to be able to navigate in space, beyond Earth's atmosphere would be quite a feat, but do-able.
To me it is easy to assume the Military Industrial Complex (made up of powerful company executives) is in control of all the technology that was handed to them and asked to "back-engineer it". Using private companies I'm sure would make it a good way to launder the money needed for such a program. Plus, there would be no public oversight. But they would have to be working hand and hand with the military. It would also explain why the United States military's lack of interest with going into space, not to mention other planets. Because they're already doing it.
But the cockiness of the group mentioned above, is what cracks-me-up. Don't they know, in the end they'll get burned? History has shown this time and again-they wont escape destiny.
I understand why they hide it. Because if they opened one can of worms, they'd have to open all the cans of worms. And then to tell the public, "Oh and sorry, but they are technologically more advanced than us and can easily do whatever they please. We are defenseless. Sorry." There would be mass panic. Plus, it would destroy several people's mind-set that "We" are not the most advanced evolved being in the universe. *snort* That always makes me roll me eyes. In my book that thinking will go down with, "the earth is flat" and "the sun revolves around earth".
Will man's ego ever learn?
On the other hand, if the MIC and Government just ripped that band-aid off, the combined intellect of the human mind is more likely to come up with a viable defense system than MIC trying to do it on their own. Humans are better at doing things together, than apart when there is a shared goal to strive for.
But I do believe we are still being observed by "Them". We are on the brink of entering into the next stage of our evolution. Either we'll destroy each other, or grow. It's that simple. So they are coming to watch to see which way we'll go. Don't get me wrong, I don't think all E.T.s benevolent and believe in non-interference, because some are coming to exploit our planet. Then there are other E.T.s who have stopped watching altogether, because they're disgusted with us. They think we'll fail to move forward and destroy our planet in the process. Which as an outsider, I would think that, too.
But all there needs to be is one cataclysmic event that changes the focus of everyone on the planet, then stand back and watch how old rivalries vanish.
I'll give one example. When 911 happened, New Yorkers for weeks after, were the nicest people on the planet who all with a common hatred for one person. Religion, age, race, gender, political standing, sexuality, financial status, or nationality no longer seemed important any more.
Mint Chip Ice cream, Krispy Kreme donuts, homemade pizza, pralines, Chinese chicken salad...mmmmm!