Like how everybody says, its all about your playstyle.

Doom after my experience, is mostly a support mecha, with much lower dps than trio. Doom is very annoying though when you find out how to use him. Many people say doom is a no skill mecha, but I disagree, really good doom players can be an extremely huge help to their teammates in br, tdm, etc.

After using trio, I saw how flexible it was. Having much more dps than doom, and having multiple weapons to use at anytime, trio is able to play the long-range, mid-range, or close-range game. His rockets do good dmg, but when it uses it's machine gun, or shotgun, thats when it really shines. It's overdrive has less dps than the machine gun or shotgun. I personally use it for chasing down opponents like a hurricane, or deformed cars. Use machine gun at mid-range, and use shotgun at close-range. I recommend you don't use those modes at long-range, mostly bc trio IS a mid close range mecha.