I vote for "argh" (h is silent). "Grr" is used a lot too, that's true. As far as my own feeling goes, this is mimicking the sound of a growling animal and therefore focusses on irritation, anger or (growing) aggression, whereas "argh" can also just be resignation. (Or anger about something unnecessary, irritating, or unnecessarily irritating). I think it's related to moaning. If you're just demonstrating your reaction to others around you, you'd say the whole "word", but as more as you get angry, the g part tends to fall silent as you focus on the r. Haha, and when I think about it, if you were really out of your mind for anger, you'd also drop the r :D

IMO the German equivalent would be "Grr!" in both cases, but I'm looking forward to other natives' answers.