I get different keyword rankings depending on what tool I use. I've recently started checking my keyword rankings on 4 different tools: 1. RankChecker by SEOBook 2. RankTracker by SEOmoz 3. Google SERP (logged out, deleted cache, geo-location United States) 4. seocentro.com's free online rank checker
My keyword rankings are similar when I use RankTracker by SEOmoz and when I just use Google and type in my keywords.
When I use RankChecker by SEOBook and seocentro's online tool, my rankings on those two are about the same.
My results for (Google SERP and RankTracker) vs (SEOBook and seocentro) are vastly different... a difference of 10 to 40 positions.
Which one should I really rely on and use as my baseline?