Picture from Wikimedia Commons.
1. General information
A small list of search engines. These are my preferred ones. There are many more, but these I find most usable.
In 1996 when I first started this listing, the search engine market hadn't quite settled yet, today - you have to consider your privacy when using a search engine.
2. Ad tracking
Today, ad-tracking is an issue. Google for example uses its ad network to server customized ads to all it's users, depending on your previous search history, your interests as specified on the social media sites you visit and so on.
In many cases this may be practical, but keep in mind that on the internet everything you do is remembered for posterity.
Read more about ad tracking on https://en.wikipedia.org/wiki/Ad_tracking.
Information about opting out of Google's personalized ads can be found at https://support.google.com/ads/answer/2662922?hl=en.
3. Privacy in the EU
In the EU, there are however laws that guarantees your right to be forgotten.
Read more about that at https://en.wikipedia.org/wiki/Right_to_be_forgotten.
4. Vaguely related stuff
"If you are not paying for it, you're not the customer; you're the product being sold"
Source is disputed.
This post from 2010 is considered to be the original; https://www.metafilter.com/95152/Userdriven-discontent#32560467.
But this one is said to have introduced the concept in the 70s; https://preview.tinyurl.com/freemium-concept.
5. Search engines
5.1. Privacy emphasizing search engines
No, trackers, no ads, all users see the same search results.
5.2. "Regular" search Engines
A search engine searches through a single database as opposed to a metasearch engine. Different users will see different search results.