With the side looking imaging, the larger the display, the better. That is because you choose how much coverage, unlike 2D sonar and the downlooking imaging that is based on the depth.
Don't know if Garmins are as adjustable as Humminbirds are, but if similar, it is a great fishing tool as well as a search tool. I use Side Imaging at the bow a lot more than 2D sonar and rarely use Down Imaging. Being able to see "over there" while fishing has led to a lot more success with catching than just seeing "down there".
Also depends on how you fish and how deep.
Humminbird Helix 12 CHIRP SI, 1198c SI, 1198c SI, ONIX 10 SI NT, Helix 7 CHIRP SI GPS G2, SOLIX 12 SI, 360, RC-1