My easiest has to be the far-eastern twelve-pin cylinder I got off of ebay and is described here:
viewtopic.php?t=17739
It has three sets of 4 pins spaced 120 degrees apart from each other. The keyway is completley circular, and at least 6mm in diameter.
Tensioning from the back (if fitted to a door you'd have to knock up some form of tension tool) each pin can be seen and manipulated easily, you can very easily feel the pins set, and there are no security pins.
I can pick it in under a minute. To fully turn, you have to pick it three times, but you are still looking at around 2 minutes to get it fully turned. A plug spinner would mean you only had to pick it once.