Avalon went with a very simple chip on a large(110nm) process. I imagine this strategy gave them very high yields out of the wafers because of the small chip size. This came at the cost of a large PCB to route to all the chips. BFL appears to be going the other way with a few very large chips based on a smaller(65nm) process. This should give them better power efficiency and more hashing power per chip at the risk of random manufacturing defects giving them fewer of these chips per wafer. Of course one hopes for 100% yields but that isn't always the case. We'll see how this all plays out very soon.