[@Dark Cloud] it'll be a tossup considering Domic is also a barb, so if he can get his rage off he's just as durable. Plus Domic has better AC. Zagren would need to win initiative, crit, and roll very well for damage to win by turn two. And considering they're both barbarians, reckless attack is going to be a given. So Domic's 17 AC vs Zagren's +6 attack means Zagren has about a 45% chance to actually hurt Domic, compared to Domic's +5 attack vs Zagren's 14 AC, which gives Domic 55% chance to hit. 

Ultimately it boils down to who wins init. Zagren's acid breath will get through rage resistance but Domic's danger sense gives him advantage in the Dex save and +2 Dex is decent, especially with advantage backing it up.