As the title suggests I'm trying to find out which unit is the best bang for your buck? The Humminbird is about $40 less expensive than the Lowrance. The boat I'm getting has an older Humminbird fish finder already, if i went with the Humminbird could i use the same wires already in place and just swap out the old transducer for the new one (or would the new transducer require a different mounting bracket)?

Humminbird's power cord has been about the same one for many model generations in two versions.

PC-10 is just the power cord

PC-11 has a built-in choke to help with possible RFI. It also has slightly larger conductors.

The plug is the same. I have several of both types.

buy the bird

Forget to add that the transom mount has been the same for a long time too. 

Transducers with XNT in the model name use the same mount.