Best one is probably (in my opinion) selfhosting a searxng instance. It takes results from a dozen of engines (you configure which ones) and merges them according to the configured weights and some algorithmic magic.

If you use public instances, the owner might have tuned the results to suit themselves and it returns garbage for your usecase. And also they frequently get timeouts because a lot of people use them. So don't get turned off by trying a couple of them.

Since I started running my own private instance I am super happy with the search results.