I made this change, but in the opposite direction: Home Assistant to Hubitat. But when I started using Home Assistant, Hubitat wasn't around (or at least public) yet, so it was the best of a bunch of "meh" options at the time as far as I was concerned. 
My primary goal was to move away from SmartThings and the cloud--and cloud problems--that comes along with that platform.
I've actually still kept both around since switching to Hubitat, however. Even after I got all my "real" devices moved to Hubitat, I kept many integrated into Home Assistant and some automations on Home Assistant too until Hubitat got things like a Hue Bridge integration (seems like forever ago, but it wasn't in the first few releases). That part was out of necessity. But there were some things I liked, mostly Home Assistant's built-in history graphs. The data is all there in Hubitat, but there is no built-in way to do anything quite like Home Assistant does by default (however, Hubigraphs, a recent community app, can perform this function now--but haven't used it yet and won't until I have time to look at the code and see if it follows my preference to read event history on demand, e.g., when I load the page, instead of subscribing to all device events...I'm picky like that).
Back when Home Assistant was my primary "hub," I couldn't get all Zigbee devices I had paired. Support for them was...mixed. I think that's gotten better (I don't remember seeing their "quirks" implementation, similar to drivers on Hubitat or DTHs on ST, back then, for one). I almost switched entirely to Z-Wave, which fares better across platforms (Hubitat and SmartThings are the only ones I find comparable on Zigbee here, and they're far ahead of anything else I've used; Z-Wave works to at least some extent almost anywhere), but the lack of good, fast motion sensors in that space was a setback. But after a few months, Hubitat appeared on the scene, and it was exactly what I longed for when I was on ST, and eventually all of my devices and automations got moved over.
I've still never been able to let go of Home Assistant to this day, though--those history graphs are pretty nice. But being pre-1.0, they do occasionally still make breaking changes, as mentioned above. Recently, I had to figure out how to re-do all of those as part of a Lovelace "dashboard" instead of the old component in the "states" UI. That was not fun, but I decided to re-do my entire installation from scratch instead of using my old config file I'd been dragging around (and manually editing) since the beginning, and I was shocked to see how much that has improved. I didn't have to edit any config file to get anything done until I started wanting to create "template" devices instead of using entirely "real" devices, and I imagine lots of people can now use the platform without doing so at all. (I never got the hang of their built-in YAML automations when I used it so I went with AppDaemon, which definitely requires code, but I'm again guessing many people can get by without that...)
Like you, I'm using the unofficial/HACS Hubitat component. MQTT is another option, and there's three ways I've seen to do that, two of which I've tried, but neither of which I've been quite as happy with (all good things to say about everyone who's contributed any, however!).
I have seen a few people keep automations on Home Assistant while using Hubitat as mostly the "radio." I'm happy with letting Hubitat do both, though Home Assistant certainly has more (nearly all unofficial) integrations that some people like. Most of my devices are Zigbee and Z-Wave, which Hubitat does a much better job with. So whichever way you choose to do things, you won't be alone!
