Suppressive Fire (I posted a lengthy (maybe too lengthy) thread in the Gamemasters section outlining a wicked tactic to use with it) is a great tool, but it really turns the Heavy Stubber into an excellent NPC weapon with limited repercussions should the players be able to get their filthy hands on it.... in the hands of a player, there usually isnt much demand for suppressive fire in my experience, primarily because player characters tend to be able to kill most opponents relatively quick, wheres said opponents already are, individually, weak, and there is little need for further pinning.
Of course, occasionally the roles are reversed, but in my experience, most fights the players are not interested in drawn-out tactical firefights, because these really play to their enemies strength, not their own (superior numbers, ammunition cost, sometimes even time-critical events like timebombs, self-destruct mechanisms or a lictor catching up
)
So I guess the Armageddon, all said and done, is the superior choice for a kill-oriented combat character unless he goes up against heavy armor. The stubber is a great NPC tool and has its uses, but usually too specialized to be worth the added weight etc.