I find Rank Tracker quite fast than others I have come across in different aspects. Although it seems the keywords limits are on lower side. They are enough for small use-case. Also, those are tracked daily so that compensated a little. Also i like the little informative graphs on each page. Haven't tried Website Auditor.
I am missing email alerts on keywords position change, but as it is in roadmap. So I am okay with it.Overall A good tool for an LTD.