There are different scenarios and different needs. Trust-wise, the enemy of your enemy may be your friend. Dodging legal liability can be an asset too, if you are dealing with evidence against the government, or powerful people within your jurisdiction. Wikileaks fills a similar role. And archive.org certainly isn't trustworthy with respect to US political influence. They are trying to rewrite history, they will purge the archives, too.

For the average case, you shouldn't fully trust any one service IMO.

BTW, there is a neat browser add-on, which lets you search across various archives: https://github.com/dessant/web-archives