I'm currently using the TangoDown battle-grip. Can't say that I like it.
Not saying that it's a bad grip, but the smooth frontstrap, lack of palm swells or finger grooves, makes it hard to stay on when my hands get sweaty.
I've handled an ergo-grip, or two, and thought they werer relatively nice, but a bit thin in the backstrap. Now, that rubber-overmolded Hogue grip is sweet. I got to shoot a rifle with one and it filled the hand nice, providing plenty of tackiness for grip and a palm swell that fit me just right.
Of course, all of this is subjective. I'll probably be switching my TDBG out for a Hogue, but I'm not in a big hurry to do it. Were I training regulary with the carbine, using it for work, I would have done it by now. But, I'm not. I'm just a joe playing with an EBR.