WordStream provides you with trends on your account performance in a single snapshot, it doesn’t provide you with a root cause analysis of why things might be going south in your campaign.

With Optmyzer’s PPC Investigator you can ask a question related to your account KPI’s and linked to a specific campaign to establish which areas you need to focus on

WordStream provides an overall snapshot of your Quality Score, but doesn’t tell you which keywords need improving, or what areas those keywords need improvement on.
With Optmyzr’s Quality Score Tracker, you get an account Quality Score snapshot as well as the keywords and their related problems that need attention.

I have used both Optmyzr and WordStream, It's all depend what you objective is, both as some great functionality.