Good points.. I mostly use google flights to search, but often book on either the airline site or on expedia. I think I usually see the same published prices and book in the place that is easy to book.

The most useful feature for me is google's price/date grid. For personal travel, I'm flexible with dates, so I always use that to just find when flights are cheap. For work, I try to find the best price, but I'm not super picky since the company is paying for it.

I feel like the travel site UIs do a good job of summarizing all the info and putting it in front of you.

Do you want the agent to book it for you? Or just find it?