Well, I disagree. Estibot offers more low quality information. Their appraisals are dumb and random. They place too much value on search volume. The are so many trash TLD one worders which get appraised at five figures. Their comparable sales are also dumb and random.
GD appraisal has some sort of algorithm and it often shows domains "similar in spirit" which is actually impressive. This is especially true for brandables. They can pull off some similar sales even if the names are really different. Estibot, on the other hand, doesn't recognize brandables at all and pulls completely random domains. GD's tool is far more advanced.
In my view, estibot is 100% useless while GD is only partly useless.