Good afternoon,
I would answer all of the above if it were an option.
I use Estibot and Godaddy together but as 99% of my names are registered at GD I tend to lean on theirs more.
They are guides only and until the day that one robot and one human check every domain name together it will never be 100% accurate.
I probably also use resources that surround me every day such as social media, TV, internet and NP especially to keep an eye on past performance and future potential.
Keeping an eye on what is currently selling helps to identify key trends from the past that are now coming to fruition and it also gives a guide on how long to hold a specific niche domain name.
Regards,
Reddstagg