They should all show fish/structure. Where the brands will differ is in the graphic user interface and menu systems. You need to consider if you want traditional sonar, down scan imaging, GPS, side scan, etc. Don't forget to budget for a battery and mounting system for the display and transducer.
You could go to Cabela's or Bass Pro and scroll through the menus on the display models to see which has an easy interface. Something like the Lowrance Elite-4x CHIRP has both traditional and down scan for about $200.