Most brewers will probably tell you that the most efficient mash tun design is the one they have. I can tell you that I've taken mine through a couple upgrades to get dramatic efficiency boosts. I have a 10 gallon cylindrical rubbermaid and would not want anything less, in terms of volume, for my mash tun. As for the lautering, I like the CPVC manifold design I built. There are pics of it in my gallery (link to the left of the post under my name). I used to use a braided hose, but had inconsistent efficiency due to dead space left over. The manifold solved that problem. The manifold also allowed me to fly sparge. What I like about fly sparging is how consistent I can be. I can dial my efficiency within a couple percentage points of my target based on my lautering flow rate (1qt/minute gets me 77-79% every time). I could go higher with a slower flow rate, but I don't want to extract tannins and besides, consistency is much more important than really high efficiency numbers.