I use fastic! I like it because it feels a bit more playful and if you are streak motivated then you have options for saving your streak with frosties (I know that is sort of cheating, but for those 2-3 days a year for me it feels better to have that option, and I am yet to use one after 3 months, but it reassuring to have it :) ) just make sure to start using something on the day you start if you want to have the precise data ( at least with fastic, you can add data retrospectively but it will not be counted in your streak).
I also heard good about Zero, especially if you need Apple watch compatibility. But I personally found it too serious. But that might be my personality speaking 😊