I run a robust Amazon Seller account, lots and lots of SKUs, large SP/PPC spend, etc.
Sellics is a must try for ANY seller, they have everything covered. In particular if you don't have reporting in place already, which I do, but I still use Sellics because I like having this all at my fingertips from an independent source, just in case my internal numbers are bad.
You may be able to find a service that fits you better in any one area, but you will not find a service that does everything as well as Sellics does it. Plus it's all in one place, for one price.
I have contacted support on numerous occasions and had a prompt, professional response as quickly as possible