@jinha I don't pay much attention to sleep tracking but the original Sense was relatively accurate compared with professional sleep tracking equipment (only the new Apple Watch is better at detecting the sleep stages). I can't speak for Sense 2 as nobody bothered to test it yet. It depends on what you need from the sleep tracking as well. Premium features include Advanced Sleep Analytics but not sure at this moment what is Premium and what isn't (there used to be a small icon next to Premium features but now I see it only displayed for Daily Readiness so I can't tell what belongs to Premium).
I'm not a fan of the Venu line. For me, it lacks several crucial features but if somebody doesn't expect a level of features of Fenix or Epix lines then Venu probably will be ok.
My issue with Sense and Sense 2 is heart rate accuracy or rather lack of it. Most of the time it's terrible. I don't track steps or floors but usually, both Garmin (Fenix 7 but Venu line will show similar behaviour) and Sense 2 come very close when it comes to steps. Although, it isn't so easy to compare both. The main difference shows up when one performs activities which are not step-based. Unlike Fitbit (any), Garmin (any( does not count steps for such activities. If I cycle, I end up with more steps on Fitbit due to extra steps being a result of a bumpy ride. Garmin won't add any steps. The same goes for swimming, kayaking, tennis etc. Floors are generally counted the same way (10 feet/3m per flight of stairs) but again, Garmin doesn't count floors for non-steps activities. For example, I got extra 10 floors today on Fitbit after swimming in the pool. Garmin gave me a 0. On days, when all I do is roughly step-based (running, hiking) steps and floors come very close (differences like 100 - 200 steps for 20000+ daily are not significant). However, for me, a winner is Garmin because it doesn't count steps and floors when I don't use steps. You will find users who think they should get steps from such activities anyway, so pick whatever floats your boat in that matter.
Garmin doesn't have a paywall. All features are available out of the box. From a few years of experience with both brands, I can also tell that Garmin gets updates and fixes more often (especially hot fixes come quick). Fitbit is a brand for patient people who can wait endlessly for things to happen and with Sense 2 and many things "coming soon", and many things missing it will be quite a wait. Again, whatever floats your boat... 🙂
Garmin misses certain features like ECG (although, after pairing the ECG chest strap you can get it via third-party apps). There is no food tracking at all. Garmin seems to not consider it important and if one of your goals is weight management and food tracking you will need to use a third-party solution like MyFitnessPal. Garmin platform has no support for that. One of the surprises for me was that there is no even way to enter a fat percentage (this is bizarre considering users have been asking for it for ages). Fitbit platform has that part covered quite well.
Garmin Venu (and others) have 3rd-party apps support (ConnectIQ). Fitbit Sense does have apps support but Sense 2 doesn't. Keep that in mind. There are plenty of threads covering what has been removed from Sense 2 in comparison with Sense.
Important probably only for me but worth mentioning. Garmin (Venu line) supports ANT+ and BT sensors. I mentioned that Sense 2 has horrible HR. That happens to other brands, too. So how do they get away with it? They support connecting external HR monitors when the wrist sensor isn't enough and they can broadcast HR, for example to gym equipment. If you plan to exercise and want accurate and lots of data, Garmin is the way to go. If you don't really care about such data and all you want is the watch autodetecting walk or run and logging it for you then Sense will do.
Worth mentioning that Garmin does support autodetection (MoveIQ feature) but I really never managed to get it working right. Eventually, I just turned that off completely. Fitbit does that job a lot better. Lots of users rely on autodetection and getting Garmin may come with disappointment when it fails to detect walking or running. The range of autodetected activities is lower, too.
If you decide to go for Fitbit then I'd probably go for cheaper and more feature-rich Sense (with proven sleep tracking accuracy). The annoyance you'd have to live with is the quirky "button" (in my opinion, the only real improvement Sense 2 brought to that family) and of course some bad HR as Sense 2. Otherwise, you're getting a superior and cheaper device.
My advice is to sit down, figure out what you want both from the watch and software, find out what feature you can sacrifice and eventually you will find a feature set that is acceptable and one device that supports it.
