I would expect the shopping ad to have the higher bounce rate . Search ads are served based on the keywords typed. So if someone is typing in google for something particular then the relevant ad text to that keyword should show and therefore what the user is looking for. If the ad leads to a good quality landing page bounce rate should be low. Wheres with shopping ads, users only see a picture of a product and click thinking they might find what they are looking for. where i want to conclude is that. Search ads are more relevant to the user, simply because of the relevant keywords in the search query and therefore will have lower bounce rate than the shopping ad.
The answer would be - blue womens nike trainers, as a) longtail keywords tend to be cheaper b) you are able to understand the intent of the users through longtail keywords, more targeted c) less competition.