I'm a curious fellow. I always want to compare the traffic between all the websites I'm visiting. Especially when I think they have a smart product / service.
I want to know how these websites resonate with their target audience. I'm usually juggling between Similarweb and Alexa. But I recently discovered another tool - free to use - which seems to deliver pretty accurate results (based on the traffic estimates of websites for which I have actual Google Analytics data).
It's called Hypestat. The cool thing is that it immediately shows you an estimate of the daily traffic in unique visitors and pageviews (+ an estimate of the website's value in an ad-supported model). The metrics seem to be based on a mix of data from Alexa, Majestic and Quantcast.
You can also compare the results of 2 different domains. An amazing feature, I absolutely love it! See for the instance the quick comparison between StickPNG.com and PNGimg.com (we still have some room for growth at StickPNG ;-)). FYI, the estimate is correct as far as StickPNG is concerned, hence my recommendation!