Going to be pimping HB here, get ready for it...
I've had nothing but good luck with my 797 and 777 since installing last spring. The units are Interlinked together and have worked flawlessly. Anyone that is serious about their electronics and does not invest in some form of side imaging is foolish. This is game changing technology. HB brought it here, and still seems to be providing the easiest access to it. No extra hardware, no extra transducers. That magic box that the Lowrance units need is huge!
As far as the 'who's image is better' argument, I think it's a wash for most people because the majority of us will be blown away at the defaults. I've played with my 2D settings for drop shotting and whatnot but the SI has been amazingly clear from day 1.
Therefore, for me it comes down to user friendliness, build quality, and customer service. I find the HB units to be more intuitive, but that's very subjective...
The card slots on the new HD units from Lowrance bug me. Every one I've seen has seemed to develop some slop and the horizontal design is not water shedding. The HB units have a water shedding design (even though I'd love to see them on the bottom) and have a secure fastener with an gasketed seal.
In regards to HB service, I have had an interesting experience lately. They offer fantastic after purchase support via their website. New software updates are made available, for free, to any registered owners. I did have some issues updating both my units recently however and needed to send them back for repair...
They turned the units, out of warranty FYI, in 9 hours, no charge. That is a fantastic throughput. Essentially same day service outside of shipping times.
Humminbird man for life.