Flat jawed ideally, I've been doing a mixture of drawing out on the horn and longways on the face, would be far easier once I have some metal tongs with better designed jaws. The wood ones I use currently are rather naff for grabbing the square bar i'm using any way other than at a right angle and on the flat face of the bar, makes hitting down the corners a bit tricky. Small steps, but once i've fashioned a more pratical pair I hope to make an even better pair.
Re the rail anvil; i'd not dare do any modifications to it as of yet. But the half that's in the shade does seem more ground down than the other, not that much but it's noticeable in person.