I had the same decision a year & 1/2 ago it is a tough one!!
I was told most people stick with what they are use to. I like both Hum. 788 CI and the HDS5.
There are some similar features but for me the features of the Hum. 788CI sold me. I used a Navionics chip in mine also. Three main features in particular sold me on the hummingbird. 1) Customer support, 2) Switchfire & 3) Depth recognition feature. There are several other features that I love but those were the one that hooked me. (Sorry I couldn’t resist). My first year I was in a learning mode. After fishing the lake for 23+ years I though I knew it pretty well but to my surprise I have learned more every day with this unit. Well, 1) customer service, while this unit was under warranty the transducer started doing funny things. I called Hum. they sent me a quad. beam transducer in place of my duel beam transducer in a matter of days. I lost no time on the lake!!! 2) Switchfire, words cannot describe this feature until you have seen it. I can see all three layers of the thermocline when it sets up. I can see my jig when jigging for lakers. I could go one but I would put you to sleep. 3) Depth recognition. I highlight the depth I do or don't want to fish and navigate accordingly. In addition I have navigated this lake in pitch dark many times relying on the GPS and to date I have not hit a hazard. (Notice I said to date). The addition features of the GPS trolling grid etc. just speaks for themselves. I have the Navionics CD for 10,000 lakes on my PC so the additional option of adding another SD card allows you to download info and put it on the unit and visa versa.
I believe either one is a great upgrade and you will enjoy them. Good luck on your decision.