Here you can get an overall picture of how prolific particular search engines are. Marketing is one thing, but how good Bing really is, for example?
This listing shows the real hits acquired from various online services. As you can see, Microsoft, despite its two-bot approach (bingbot and msnbot) falls far behind its main rival. Second? Yes. Useful? Hell no!
I have not yet implemented any conversion tracking system, but from my manual reading of logs and reports, Google targets the audience best too.
This list is generated rarely, about thrice a year, so don't burn your F5 key. But that doesn't matter, the game remains the same for long.
Oh, I didn't even bother with Our country's largest web portal only indexes 2 (in words: TWO) individual pages of my 100 thousand. No miracle can come out of that.