Since you're in the planning stage I would check out any threads concerning both brands until you get a good hold on the unit you want the most and just pick one brand and stay with it.
Customer service with Lowrance was pretty bad a couple years ago when Linda Colt was fired. She would it when people had bad experiences with other service reps. I don't know about them since then as I have Bird units.
Either way If I was going to use the HDS units I would only keep the Humminbird in there as a backup unit. If you do it for redundancy you would not have both units on at the same time.
I would go to the bass boat central fourm and reed the reviews on each.
The main advantage to the bird is no lss-1 module to leave on the boat or get stole.
Donnald Borris from Borris marine recomends the removal of a sonar while trailering.
I keep my graph in a soft case and in the room or truck with me.
I love the tulsa made Lowrance I own 5, they are now made in mexico and have poor quality!