It's personal preference. Look at old photo's of Sean Yates and the position he set his bars at. I couldn't imagine riding with my hands in that position all day long. The tops are set at a steep downward slop while the bottoms slop upward towards him - most unusual.

I set my bars to be both comfortable and visually appealing to me - it has to look good to me. Personally I like the tops to sweep downwards slightly and generally follow the line created by the angle of the stem (I HATE the look of the upward sloping stems of the compact framed bikes - it just looks wrong to me).

The manufacturer of the bar is also important. On a track bike, using Cinelli bars, I like the bottom section if the bar to be parallel to the ground - It looks more purposful yet it is comfortable to race on.

I don't think the angle you set the bars at has any bearing on a more wind resistant position but I feel the height of the stem, out of the headtube does.