Visit a store that has them on display. Bass Pro, Cabelas, Gander Mt.
Do it on your own with no help from a sales person. Push the buttons and see which you are comfortable with.
When you determine that, purchase from a marine electronics dealer. It will be less than the big box general sporting goods places typically.
Humminbird Helix 12 CHIRP SI, 1198c SI, 1198c SI, ONIX 10 SI NT, Helix 7 CHIRP SI GPS G2, 360, RC-1