Here's the crazy thing about these sort of threads... The biggest historical keyword ranking tracker that works for various countries and multiple search engines, and 100% complies with search engine terms of service (only uses APIs), is right here on this site. In fact, our Keyword Tracker tool was around about about 6 months before the forum was started. This entire forum was started in part because we needed a support venue for our SERP tracker. About 100,000 users are using it now, and it still continues to be one of the most popular areas of Digital Point. It cracks me up that people come to the forum to ask where they can find a good SERp tracker. lol Oh yeah, it's free too. https://tools.digitalpoint.com/tracker
I would recommend you SerpYou.com - this SERP tracker has clean and easy to use interface, it's fast and accurate. It has multiple reporting features and seems so far to be less expensive than others.