So let's say you're doing an everyday search for something such as researching a new camera. Would you consider the probability of someone eavesdropping on your communication times the amount of harm they could likely cause to you using that information to outweigh any amount of improvement in search result quality? I'm not trying to be facetious — just genuinely curious if that's how your utility function works.
That would only make the decision simple if you absolutely had to use only one search engine. You could just as easily use Google's encrypted interface for insecure connections and Bing at home IF you thought Bing was better.
1) I'm sometimes using untrusted networks (e.g., Wifi)
2) Google offers an SSL encrypted interface
3) Bing doesn't