I own a fishing buddy 2 and the humminbird port. Pirahna 15.
First thing: Depth finding ability...The hummingbird is more accurate for depth because the sensor cup is right on the bottom of the boat. I used the fishingbuddy (had two of them) for the last 15 years and this summer I fished with both of them out of the same boat. The depth reading of the FB was out by two feet and that was after I added on the extra foot for the extension in the water. For all those years I fished water that was 2 feet deeper than I thought. The Hum. was bang on for depth.
Second thing: Fish finding ability...The FB gives you a fish reading below the boat and out to the side (about 45 degrees) in the direction its pointing at which is fine as long as you're only fishing in that direction. In other words there could be fish close to you in another direction that you won't know about. BUT..I think the FB is more sensitive to finding fish although it will also sound on long weeds. Of course if there isn't any there then you'll know it's fish. My hummingbird isn't as sensitive but because it has dual cones it picks up fish in every direction. If the fish are below the boat it's a solid symbol and hollow if out to the sides. If you are anchored on a dropoff and the fish is to the shallow side of you the hollow symbol will be under the line showing the bottom; if to the deeper side it will be above the bottom line. That's kinda cool. Also, when you are cruising the shoals at higher speeds it reads the fish better below you. You can't have the FB out when you're cruising at higher speeds because it wobbles so hard that you might break the bracket.
Third thing: Power Source: Both run on batteries that last a good long time as long as you remember when you're done fishing to flip one of the batteries over so that if the finder is accidentily turned on they won't burn out the batteries. FB uses 3 C batteries; Hum uses 8 AA batteries. The non-portables have to run off a huge marine like battery. That's why i didn't buy a fixed one.
Fourth thing: Portability. Both are good. The Hum. packs up into it's own little case and it's really easy to put on the suction cup. If you used it on a float tube or pontoon you'd just need to rig up a thin 4 inch board about a foot and a half long that runs down the side of your boat to put the suction cup on. The side bag should hold the sounder or rig it up so that it sits in a scotty rod holder bracket. I put my FB through the drink holder cup and strap a bungie around the top part of the sounder arm, then around the tube or pontoon, then connect it to the bottom part of the finder arm. It's very sturdy and doesn't get in the way. Put your net on the other side of the tube or pontoon.
I definitely like my Hum. more. It's more durable ( I have a number of friends whose went on the blitz after travelling down many bumpy roads dozens of times), better depth accuracy which is the most important feature of these things, it can sit right on the seat in front of you, and you can keep it running while you're cruising at top speed with your electric motor.
Hope this helps out XG