I really think they're similar, man. Armamentarium doesn't enhance ANY character abilities or perks, it just gives more ammo and one added grenade. (For the record, the added grenade perk is kind of a bag of @$$ - it takes foreeeeever to charge them both.) Praxic Fire adds Fusion ammo, Heavy ammo, and enhances super. Boosting super is kind of huge, especially for Sunsingers who have a mode switch rather than a panic button. I think they're very similar. Not to mention Sunbreakers are kick@$$, I have them on my Singer right now and it's like bossmode for PvE. Room full of enemies? More orbs for my teammies. Boss? Grenade bowling practice. Plus speed reload on any SP weapon. How do you not love that?