makko2

I used to like Similarweb as a second alternative option to Alexa gauging other sites traffic trends - even if roughly.
Lately I saw similarweb was laughably way off on a site's actual stats. Making me wonder how much way-off it can be with other sites too.

What are your ideas on these two and others?
Alexa supposedly favours* slightly those sites registered as pro accounts with them.

Any real-fact feedback on this topic?