there are pro's and cons to both . image wise they are pretty much equal . ease of install goes to humminbird with just the display,transducer and (if you get the external gps ) the gps puck.
with lowrance you have the display,transducer, gps and lss module (which needs a power hook up as well) .
add features goes to lowrance with the capability of on the water radar,xm satellite tv , weather radar (humminbird does have xm weather radar) and engine monitoring (if you have a 2002 or newer mercury)
the big one is customer service though which humminbird has and lowrance does not in my experience .
feel free to give me a call and i can go into more detail
303-8982
david