I'm looking to buy a crop sensor for my nitrogen applicator. Which sensor do you prefer? Why?

[Bnapier2015]

Im needing a crop sensor for my nitrogen/fertilizer applicator. Which of the Trimble(GreenSeeker), TopCon(CropSpec), Ag Leader(Optrx), or Satelitte Imagery do you recommend? Why?

[Jim Meade / Iowa City]

I hope you get a response, but I've not heard of these applications being mentioned here so it will be interesting to see what response  you get.