HOW TO CHOOSE A GRAPH
Choosing the right fish finder can be a challenge, considering all the makes, models, and price ranges to choose from. I will give you a few things to consider, so you can make the best choice.
Whatever you buy will be obsolete tomorrow
Keep in mind that fishing electronics are just like computers. They are necessary and helpful, but not good investments. The top of the line today will be old news in a few months. Always keep this in mind when you are making your decision. If you are one of those guys who has to have the top of the line, you can expect to spend a lot and do it often.
Get what you can afford
You probably aren't going to catch more fish just because you have the top of the line equipment. A person who knows how to use the best graph on the market should also be able to do just fine with a step or 2 below it. If you can afford the best and not have to sacrifice fishing time to pay for it, then go for it.
If you are a bank beater and never intend to learn how to use your graph, a high end graph is a waste of money. I recommend getting what you can afford, learning everything you can about it, and putting what you have learned to use.
I believe mapping (with GPS) is very valuable as a tool. It is very expensive, but worth the money. I wouldn't want to have a unit without mapping.
Transducers
Make sure you have the correct transducer for your boat. There are basically 3 ways to set up your transducer: on the trolling motor, through the hull (not on aluminum), and on the back of the boat. Consider the possibility that you may switch your unit from the dash to the trolling motor when you upgrade or if one goes out. Many units are compatible with the same transducers. If you buy an older graph, keep in mind that it may not be compatible with the new transducers.
You may have a choice to pay more for a dual frequency transducer. You probably won't have any reason to pay extra for the low frequency unless you are in very deep salt water.
Resolution
The main difference between a high end graph and a low end graph is resolution. You will pay much more for a clear picture. Below is a comparison of the same screen shot with different resolutions.
The one on the left has 100 vertical pixels, while the one on the right has 240. I recommend getting 480 vertical pixels if possible. You will be more likely able to distinguish fish from clutter. Obviously, the more pixels the better picture and bigger price tag. Get what you can afford.
GPS/Mapping
Mapping software is available in many of the newer fish finders. It is a big innovation that also has a big price tag. The navigation and mapping capabilities can take you right to a bridge, road bed, underwater pond, hump, etc. if your lake map is available. They can also make trails where you have been and help you navigate back to the boat ramp. I recommend you do your homework and make sure you intend to get your money's worth before making such an investment. I wouldn't recommend spending a lot more money for a graph with this capability unless you intend to get the mapping/GPS software at the same time.
Power
Power is probably not something you should be concerned with unless you are fishing very deep salt water. Chances are, if you are willing to pay for a decent picture, you will get enough power to display it. The more power you get, the louder the sound will be. I can hear my 4,000 watt transducer in the back of the boat from the front. Lowrance claims that fish can't hear the frequency. I am not totally convinced of that. I keep my unit on when I am mobile and turn it off when anchored.
HyperScroll™
Older units only show fish arcs at a standstill or extremely slow speeds, even with chart speed at max. Lowrance has a new feature called HyperScroll™ which is intended to display fish targets at high boat speeds with more soundings per second. Many of their newer units have this feature.
Auto range
Many units require manual range changing while in manual mode. Who wants to change the ranges while trying to drive the boat? Auto range, available in many of the newer units, is a useful feature for the fisherman who uses manual mode. In automatic mode, the ranges change automatically, but so does the sensitivity and any other settings you may have tweaked.
Backlighting
The units I have used have good lighting. However, some units aren't so good. Be sure to test it before buying.
Temperature gauge
Many units offer temp gauges as either standard or optional features. This is important if you don't have another temp gauge, but keep in mind that you may be paying for another gauge that you already have. Also, if you are shooting through the hull of a fiberglass boat, you can't expect the temp gauge to work correctly since it is inside the boat. But it seems they are more accurate than you would expect.
Shallow alarms
This is a feature that can be helpful if you are driving through unknown territory and need to be alerted when you get close to ground. However, it can also be very annoying if you have it on and don't need it on.
Other features
There are many other features that either are standard on every unit or basically useless. Fish ID is one of those features that I haven't found to be useful. I expect the technology to improve here, but for now they just translate any recordings into fish pictures - whether fish, bait, stumps, thermoclines, etc.
When the technology gets to where they can distinguish a bass from other species of fish, I will change my opinion.
Fish alarms are another feature that I have found to be not only useless, but very annoying.