First of all, the difference between TFT and LED screens is the lighting. TFT screens have CCFL (cold-cathode fluorescent lamps) back lighting, while LED screens, not surprisingly, have LED back lighting. LED backlight screens are a bit more efficient than the CCFL ones since they have less flicker. Also, LED backlit screens consume less battery.
Now, when it comes to Humminbird fish finders, most of the models have LED backlit screens, so the lighting shouldn’t be a feature to be concerned about. If you’re looking for quality image, you should pay attention at the pixel resolution, the width of the screen and whether is color or monochrome. Obviously, the fish finder models with monochrome screens are cheaper, but if you just want to locate fish via the FISH ID feature, measure depth or water temperature, they’ll do just fine.
On the other hand, if you want a multifunctional boating device, a fish finder with chartplotting and marine GPS functions, and Side Imaging for locating fish, you should go for a model with a bigger screen, with a higher resolution, like the 1198c SI Combo, or 998c SI Combo. The 1198c SI Combo model features a 10.4″ diagonal screen with a 600X800 pixel resolution, and the 998c SI Combo an 8″ diagonal, and 480X800 pixel resolution, and both provide crystal clear images of maps, Side Imaging and Down Imaging.