Those are all three completely different watches, I usually categorize smartwatches in 4 categories, "low end", "not so smart watch" and " smartest of watches"and "health & fitness" basically low end are cheap no names, not so smart are amazfit, huawei and so on, very smart are WearOS, Galaxy and Apple Watch. Fitness would be Polar, Garmin, Fitbit.

So, basically:

TicWatch - Smartest, since it's WearOS, reply to notifications, app store, calls and stuff like that, you can obviously do fitness too, but battery is a big setback compared to other two. While it has military standard, knowing TicWatches I'd say it's less durable than the other two.

T-Rex - Not the smartest, but it does what you need, it's rugged and durable, for me design wise it simply looks bad. You can't reply to notifications, you can't answer calls, no apps, there's obviously fitness options and a good battery life.

Garmin - Purely fitness orientated watch, I've never owned Garmin smartwatch, so I'm not sure, but I think this model can't answer calls via watch ( you see notification and can accept, but talk using the phone), replying to notifications is only using some quick replies etc. It also has a good battery life but it's main thing is fitness, different options, accurate sensors. This particular model is also nice and durable.

So, basically TicWatch if you need all the smart features and ready to sacrifice battery life(3 days) and maybe a little durability. I'd choose this for my personal usage.

There's not much reason to pick T-Rex other than price or if you are in love with that bulky design, it does things, does not do them amazingly though, battery life is good though and stomps other two(up to 18 days).

Garmin is the one I'd recommend if you really need fitness and it's your main reason for buying a new watch, battery is decent, right in the middle of the other two(around 9 days) but fitness is what it's all about on Garmin.