Believe it or not, even in 2016, even with the ad label, there are still plenty of people who have no idea that there is a difference between the paid and organic listings... They just go to Google and click on a link with a snippet that speaks to them.

Personally, as a search marketer, I always assume that someone willing to pay money to reach me probably has a more relevant offering and experience for me, so I am slightly biased to click on ads...

Your question should really be more nuanced. Are you talking about navigational searches, informational searches, or transactional searches. There is different intent and context with how and why people search at different times which probably results in different behavior.

For example, an informational search from me almost never clicks on an ad but either knowledge graph or a link half way down the page.

A transactional search will almost always go to a paid ad, and a navigational search will likely go to the organic listing that points to that page...unless the ad points to that specific page. (this is just my own experience.)

I'm clicking the ad! If someone went through the trouble and payed for putting their website above their website, I'll make sure that their ad budget is well spent! /s

A lot of people don't know, pay attention, or care enough.

If it's a company I like then I click the organic listing. On the other hand, if it's an ad for someone who needs the money less than google does then I do my part and donate to the google foundation.

Organic, always. No desire to encourage advertising.

(Yes, I'd be willing to pay a modest subscription if Google got out of the advertising business. No, I doubt this pledge will ever be put to the test...)