They are adorable as cubs but when adults they fierce and deadly. They will charge you down in no time. Your best bet is to run as fast and as far as you can. If there is only two paths you can take one has a direbear and one has a lv 300 Rex I would chose the Rex. But when taming you want at least two people are a rock to climb on. From there use tranq darts mostly and try not to get yourself killed.
Best utility mount after theri can gather meat and berries also this guy can get 1k weight and almost 900 melee with enough lvls I know this because my bear ( name is teddy the bear) is stronger than my 209 Rex