be best for your current fishing environment is that lower frequencies travel better over longer distances.This will make them better for deeper water, while higher frequencies give a better return in shallower waters (better suited for float tube) at least for me the water I fish in are anywhere from 10' to 30' ranges pretty shallow overall.
Now let's talk cones, higher frequencies tend to operate in a narrower cone than lower frequencies and despite covering less of the bottom tend to be the better choice in shallow water. So the cone can be wide or narrow and if they are near then what you see on your fishfinder is more then likely pretty close to you if not under you. While a large cone will give more distance covered and in turn what you see might be in a larger area (further away). A good option for us as float tubers would be a 200Khz and a narrow cone of about 2 Degrees. The reasons for a narrow cone is we are slow movers and concentrated on what is near us. If we moved faster we could use a wider cone to cover more area.
If you are operating in shallow water and want a greater view of the bottom, some manufacturers offer a high frequency with a wider cone than other manufacturers of similar frequency. When selecting a transducer you must ensure that the frequencies and cone it operates on are appropriate for the depth of waters you will be fishing in and also match the capabilities of the fish finder. To understand the heart of the fish finder you will better understand how it works and in turn get better use out of maybe one of your more expensive items