Google, because it has a simple search engine page and a personalized page packed with features, instead of Yahoo thrusting everything at us. Bing I've never really used.
Google, hands down. Quick searches, plethora of results and quick loading. Never used Bing so can't comment on it. I no longer use Yahoo anymore (except for Yahoo! Answers, which is a different case altogether), it's webpage takes too long to load in comparison with Google, not to mention unorganised, also there are fewer search results and inaccurate ones at that.
When it comes to email, I have to say yahoo, though yahoo has too many random apps or whatever you can use that I find to be useless. Search wise definately Google, though Yahoo is close, behind. Bing is alright, its the only image search engine I can use at school so I don't mind it.