Aman A.:
Those who have hardly any experience with Vajrayana practices are in no position to compare the two practices. Only those who have done both can know better.
There are some scientific studies as well which show remarkable results which were conducted on Vajrayana monks.
Disclaimer: In view of those who have only practiced Hinayana, what I say may not go well. It may be better for them to first try Vajrayana practices and see for themselves.
There are also plenty of scientific studies on vipassana practioners. I don't know of any comparing the two.
I think that what you're saying amounts to saying that one form of vipassana is objectively better than another form of vipassana. In what way is diety yoga not a form of vipassana? As mentioned, my former Vajrayana teacher claimed that it was.
For what it's worth, I have done both (and other things) and I know a lot of people who have done the full range of Vajrayana practices for decades and a lot of people who have done various styles of vipassana and jhana-oriented samatha. I do think Vajrayana is very effective, but I also think it's very complicated and requires a lot of dedication to lead to lasting tangible results. I'm aware of the explanations stating how and why the highest Vajrayana practices are extremely simple, however those practices require mastery of their respective foundation practices (which I've practiced, but hardly came close to mastering) in order to achieve sufficient concentration and energy manipulation skills.
While I stopped doing Vajrayana in mid 2007, I've still done more Vajrayana practice at this point than vipassana practice. I wouldn't say I've done any Hinayana practice, because I don't think that such a thing as "Hinayana" actually exists anymore. As far as I know, it's a derogatory term for proto-Mahayana sects that died out a long time ago that Lamas like to use since they rely on literature that dates back to when those sects existed. (I realize it also refers to certain foundational practices that come before ngondro and a specific outlook on the practice.) I was able to get the 1st path through Mahasi-style vipassana after a few months of practice (two months of an hour and half a day, plus a month-long retreat) according to Kenneth Folk's instructions nearly two years ago. My success at the practice (which is fairly commonplace by the standards of this board) is probably due to understanding the practice better and being more mature and serious about it than I was about Vajrayana. That being said, I do still think this says something about the claim that lackluster Vajrayana practice is still superior to any non-Vajrayana practice. Doing Vajrayana well is not easy.
Considering that for both practices I had some of the best and most reputable teachers in the world, and asked every question I could think of, I think one key might be that one practice is simpler than the other and suits my personality better. Given more work on visualization and the vipassana tricks I know now, I don't see any reason why I couldn't have reproduced the same results with diety visualization and other Vajrayana practices I was taught, though ultimately, that just means that diety visualization is another form of vipassana, as my old and very well-respected Nyingma teacher once stated (see my previous post in this thread for the quote).
As can be seen on this board and the KFD board, a lot people have managed to take it much further in less time and are able to do practices that resemble Mahamudra with continuous attention and have gained the realization of emptiness, all through variations on Mahasi-style vipassana or using practices that used noting as a foundation. Of all the fellow Vajrayana students I've met, not counting monks and non-monastic Rinpoches, only one (a very dedicated practitioner from Germany) had managed to gain the realization of emptiness. I can't say anything about them gaining path attainments, since Vajrayana (or at least Nyingma and Kagyu) emphasizes different maps and doesn't look for the same things for measuring progress. All the same, noting-based vipassana does seem like a very effective and quick method to achieve things that are considered meaningful achievements by Vajrayanists.
Considering that both systems deal with paying attention to the senses, and paying attention to them in a moment-to-moment changing sensation sort of way, I suspect that done properly, both lead to similar results.