Don't really care for the appraisals much, maybe the only benefit I see to them is that they help narrow down domain lists a bit.
I've been playing around with both and DomainTools provides lists of current, pending delete, and available domains all in one list. You can then break them down by category (page rank, age, DMOZ, Yahoo, etc.) (Free)
Estibot provides lists according to their status (pending delete, redemption period, available, NameJet auctions, GoDaddy auctions, etc) with their appraisals. ($40/month)
Still playing around with them to see what makes Estibot worth the $40 a month versus using DomainTools...