One month ago I researched third party survey tools (ex. SurveyMonkey) as well as just building what we needed in a Marketo form. Since SurveyMonkey had an integration with Marketo, I reached out to them via their contact us form, but never heard back from Sales. So I opted to just build the survey within a Marketo form myself and it turned out to serve the exact purpose we needed. Several other pros for Marketo as opposed to a third party tool were that we avoided additional costs and a potentially lengthy implementation timeframe.
Actually we've integrated Survey Monkey at our sandbox instance. it was worked well. However, they've changed company strategy and very limited support recently, so I'm looking for another suitable survey tool vendor now.
We have used JotForms Online Form Builder · JotForm not only for ourselves internally but for some of our customers. Even though there is no standard integration with Marketo they have an API and you can integrate it.
In terms of integration it depends on what you want to do, of course.
.png)