I'm new to fixed gear bikes, I do realize all the sub $600 bikes have their faults and compromised components, these bikes still seem like a reasonable place to start for many newcomers who don't have the time, tools or skills to build their own.
I went with a Pista, I haven't had as much fun on a bike in a long time, it's light, fast and handles great. I'd get out there and try a couple, you'll figure out what you like pretty quick.