Personally I myself wouldn't get anything hyphenated. I dislike them and I know most people dont even think to type them in that way. To me it would be a turn off in regards to type in traffic. As for search engines, I am not really sure which has preference. But I myself would probably go for the .net instead since it wouldn't have the hyphen. But then you will want to ask yourself what kind of name it is in the first place for it to already be in use? Is it being used by a company? Are there any trademarks on it? If it is just taken and parked as a .com, then the situation would be moreso in your favor. But to me, I would rather pay more to have a non hyphenated .net vs. a hypenated .com.