IMO the best combo is SurveyMonkey + a custom Marketo integration built using the very nice SM API. (Note I’m not talking about the SurveyMonkey Marketo native integration, which is very good but requires their $$$ Enterprise plan.)
This’ll give a nice balance of survey building/taking/reporting features, affordability, and visibility in Marketo (creating survey Custom Objects, setting program statuses, triggering personalized email follow-ups, etc.).
Another option is of course eschewing a survey-as-a-service platform entirely, instead building a survey-like sequence w/Marketo forms. You can do almost anything as far as the UX that way, provided you have a good JS developer. But you won’t have a visual builder — it’ll all be in code — and reporting may require pulling data from Marketo via the API into Excel, etc.. Even as a Marketo developer I have to say that’s suboptimal.