For me, Serpwatch seems to be the simplest rank tracking solutions out there. The interface and UI are fantastic and very easy to read.

I'm able to offer my clients a full white-labelled experience on MY site without paying hundreds of dollars per month, and I get accurate rank tracking and reports. We can send the individualized dashboards to clients via simple URL so they can check their rankings each day which is fantastic for those high maintenance clients. You can see which way rankings are trending at a glance which is a great way to spot problems in campaigns and address them proactively. The daily rank tracking was super important and they do a very good job at it. The ability to go back 30 days, 90 days, or all time gives you some very good options for comparing rankings. You can also pick specific date ranges which gives you even more flexibility to show clients what is happening in their campaign.

I've fully switched to using Serpwatch for all my rank tracking and site audits, and it's been great.