I bought the highest tier. If you're reading the reviews and questions like I did, note that they did listen to the users and increase the number of competitors. I put a lot of value in the company's response to users, so that was the main reason I decided to buy right way.

I also have Nozzle, SerpWatch, and Ranktracker, so I was probably going to buy at least the lowest tier anyway, but it was worth it to upgrade to the max for their future potential. The rank tracking is pretty straightforward. The SEO analyzer isn't very detailed yet, the page returned from the analysis is pretty short, but they can easily improve it over time. One nice thing I like is the Sistrix visibility tracker. The big thing was when they listened to users and increased the number of competitors, I bought Tier 3 just for that so I could max out the competitors per project.