I own Lowrance and Eagle electronics which I consider top of the line. I don't see much difference in the two brands, the same company makes both, they use the same transducer, the Lowrance has a bigger screen which makes it easier to see, both during the day and at night. It packs a whopping 3000 watts of power to the Transducer which allows you to see better detail of the bottom and structure. Both units have split screen and zoom capabilities, these I like, you can tell the difference between a boulder and a Flathead. You can zoom right in on a piece of structure, very important because a Flathead sits on the bottom resting and the grey scale will tell you the difference between a soft bellied Flathead and a hard rock. Read the owners manual of the fish finder you own it will tell you a lot about your unit, but there is no greater teacher than spending time on the water with the unit, I learned how to read one by fishing Norris Lake in Tennessee for stripers, the water is very clear and you can see what's on the bottom and reference it to the fish finder.
First, do you believe your sonar unit is showing you exactly what's down there? If you answered "no" don't feel bad, a lot of fishermen feel that way, believe what your unit is telling you and you will get real good at reading one of these things.
The price of the Lowrance is in the upper range. I'm glad I spent the extra money and purchased the Lowrance it took me almost three years to learn how to read it but I made it, boy that first year I fished for a lot of rocks, and didn't catch a lot of fish, now I still may not catch allot of fish but I know a fish between a rock.
I used to run it on Automatic when I first got the thing, there's something about all those fish looking symbols that just attracts a fisherman, but you know a stick, weeds, rocks, anything that passes under your Transducer will look like a fish, plus the fact is it takes a lot of power to make those fish symbols, if you like seeing all those fish then go for it, I run it in manual, takes less power to make those arches and you generally can see the size of the fish, being baitfish or the predator. You will not see those great looking arches on the screen like you see at the fish shows. Sometimes they are half arches, just a dot or you may see a complete arch, if you do then that fish has passed directly under your Transducer.
Look at the first picture, I know it's kind of hard to see, the reflection of myself standing in front of the finder messed up the picture, but it's hard to shoot photos in a moving boat. I'm running a flat area with an irregular bottom, water depth is 47 feet and those blips along the bottom are fish, to the left are some baitfish that look like they are relating to a small hump in the river bottom, note that the water temperature is a balmy 56.4 which isn't bad for November 30th.
Next picture we are running the same area of the river, see that hump, it's on the down river side, we were on the flat then we moved up on the hump, and we are marking fish, but most of these fish are resting, laying behind the hump out of the main current, that one on top is probably an active feeding fish. This hump had a depression in the center but no fish were there.
Look at this picture, same hump but we are on the front side of it, the river is flowing over the top and WOW!!!!! Look at the fish! These are active feeding fish on the front side of that hump, at the 44 foot mark there is a school of baitfish, Baitfish show up as clouds, or large masses on the screen. We anchored down at this spot, the wind was blowing hard and we had trouble keeping the boat in one spot with just the front anchor, but catfish will find that rope if it is dropped down on the backside so I try to refrain from using it. We caught several Flatheads and channels off of the front of this hump. They hit both live and cut bait. As soon as the bait settled on the bottom they moved up on it.
Keep this in mind: Most active river fish feed on the front side of a hump where the river is flowing over it and rest on the back side away from the current.
Here's what most of them took, a fresh piece of cut shad, I always leave the hook exposed, I really don't think they know it's a hook until you set it, but shad scales are tough, and if the hook is left in the bait and the point is not exposed, the scales can deflect the hook point away from the catfish mouth.
A couple of other things, run your sensitivity so that you pick up a little bit of artifact, but not a lot, I have mine set at around 65-68% range on my Lowrance and a bit higher on the Eagle. Before you put your boat in the water check the angle of your Transducer, these things can get bumped around when you are trailering, wipe the face down on the Transducer to make sure nothing is on it, when it's in the water dirt can show up as artifact on your screen, when you pull your boat from the water wipe down the Transducer, the oil slick from boat motors can adhere to the face and will destroy it after sometime. Here's the picture of the pole holder I made, it's made from regular pvc pipe and it has quick removable pins so I can take it down when I'm trailering the boat down the highway, with this set-up you can fish four poles straight out the back of the boat, and any little tap on the poles is highly registered, it makes it kind of nice because you can pick the pole up and rest it across the main bar and wait for the line to tighten up. There are two pins that are threaded into the pvc to keep the rods in the upright position.