I would go with the 1/2" autosiphon. I have a 5/16" and have been wishing they made a larger diameter one, I wasn't aware they did.
5/16" is just too slow or perhaps I am just too impatient.
MATT - 65g in 2k8
3rd Circle Brewery
Ferminatin' - Route 666 Pale Ale
Figurin' to do - Oatmeal Stout, Gueuze, Belgian Blonde, Mild, English Pale Ale, Weizenbock