The verdict
If you run a software product and need to know who uses a feature and where new users drop out, pick Mixpanel. If you need to measure satisfaction, run NPS, take an employee pulse or research a market, pick SurveyMonkey. A small B2B team with a live product should start with Mixpanel, since you cannot ask good survey questions until you know where the problem is. Once Mixpanel shows a drop, a short survey to that cohort is a good way to find the reason. A team with no product to instrument, only customers and staff to ask, needs SurveyMonkey.