I was researching this the past week....I was looking at Time Atac, Shimano and Look.

Look weighted less, fair price and good looks BUT the quartz doesn't have float adjustment so I didn't choose it.
Shimano's M520,30,40 had great reviews but some fixed riders said that they had some unclipping situations and that scared me (I know that it could very well be because of the rider, worn cleats, etc) but the
Time Atac Roc or Aliums had better reviews from fixed riders so I went with it.