They all work. As far as which one to get is up to what you need it for. The more details, the more depth you want to use it in, the more power and resolution you will need. I am a fan of eagle/lowrance stuff myself. There are plenty of good depthfinder deals on ebay, portables too. I have made some great purchases in the past month there saving up to 75% on new stuff.
please fish responsibly