I wish I had gone for the Polo one instead of the 206. That's more to do with space (mini conversion).
A 4 2 1 is apparently better for lower down the rev range than a 4 1.
So the Polo will be better for a road car but the 106 will be easier to modify.
It would be handy to get a cardboard template of each of the flanges and offer them up to the head to see how close the port spacings are. Or buy an exhaust gasket for each and then sell them on Ebay when you are done with them.