I use the Helix 7.
I think the choice will come down to personal preference. Before you buy consider:
Will it be ice use only or used on a boat as well? Humminbird Helix allows you to do both.
Is mapping important to you? Humminbird comes loaded with basemap which I find sufficient where I fish, and is upgradeable to Navionics and LakeMaster. I can GPS mark spots where I catch fish and capture screen shots. Plus track my paths so I can get back to my holes even in driving snow.
Is budget a limiting factor? Do you plan on upgrading in the near future? If yes, then buy the one unit you can live with for a long time.
How about battery life? I can fish for days with my extra batteries and solar panels, but if you are limited, the Humminbird unit has a power standby feature that allows you to sleep the unit while going in between holes to conserve battery life.
Not that familiar with the Garmin unit mentioned, but had a Lowrance Ice4 and the Helix blows it away.
Finally, after using different manufacturers' menu interfaces, I find Humminbird to be the most intuitive which can be critical when you don't have time to mess with buttons when a fish is under you.
Finally, getting a hands on demo can help sway the choice one way or the other. Hopefully you have a large sporting goods store near you. It would be worth the trip.