You don't know if it's the best because there is no competition to discover better info. All other websites are presented with only 2 or 3 lines of text (search results) and have no free access to presentation forms that googles own content has.

Everything's "based on merit" until merit doesn't line up with the company's interests anymore.

I use google translate and maps and images all the time, so them showing up at the top of the results page isn't inconvenient for me, but sometimes when I use them I get results that are actively bad and I have to go seek out other services. There are probably many cases where I get bad results and am not informed enough to recognize that the results were bad!