I've recently starting riding my horse in a curb again. I have an Argentine, but I don't like it. (Too much bit, because of the broken mount piece. Lots of pressure points. I'd rather spare my horse's tounge from the nut cracker action in combination with pole/chin pressure.)
I asked a friend what they thought I should get. They loaned me with Myler curb to try out. It's got a bit of a port (I don't know anything about Western bits, so I cannot say whether that's a good or bad thing), but I like how the sides move independantly from the middle joint. Sometime's my horse has flights of fancy where she forgets to neck rein, so I have to correct her with a direct rein.
Myler Bit Stainless Steel HBT Shank