I responded to a post on one of the Humminbird Facebook groups and thought I would also post it here for input and debate.
Here was my response:
Most people would agree that Humminbird still has the best Side Imaging of the 3 leading freshwater fishing electronics producers. As for which Humminbird model has the best for side imaging, it would be those with SI+ (Helix G3/G4, Solix G2/G3, and Apex), and all of these will be very close to each other.
There are those who claim that the Solix and Apex SI+ models have better imaging because each imaging piezo is grounded separately and, therefore, produces a cleaner image. I've never had Helix so I haven't been able to do that comparison myself.
In my personal opinion, the Apex has the best SI+ because SI really benefits from the Apex full HD resolution... the highest resolution of the Humminbird models. Although things like 2D and Mega Live don't really benefit much from the increased resolution, SI+, DI+, and Mega 360 definitely benefit from the higher resolution. On those technologies, fine details can make a real difference.
As for screen size, bigger is definitely better when it comes to SI... Especially if you want to display multiple images on the display at once.