Doughnuts or Donuts? having the munchies!

Have you all wondered which term was the appropriate one? Or simply, where lies the difference in their usages? Well they were pretty much my favourite snacks so and I've always wondered so I decided to run a search for both word forms in the some of the dictionaries we have available.
Based on the Macmillan Dictionary and the Longman Dictionary, 'doughnut' was the generally more common variant whereas 'donut' was mainly used in American English. Here are the lexical entries.

Macmillan:
definition of

donut

noun [countable] mainly American
a doughnut(main entry)

Longman:

do‧nut especially American English

x-ref another spelling of doughnut

Most other dictionaries also agree that 'doughnut' was the more commonly used variant, for that was the main entry, with 'donut' listed as the variant.

Oxford English dictionary
Also donut.
1. A small spongy cake made of dough (usually sweetened and spiced), and fried or boiled in lard. Freq. made in the shape of a thick ring.

Merriam-Webster:

Main Entry: dough·nut

Variant(s): also do·nut \-(ˌ)nət\

Function: noun

Date: circa 1809

1 : a small usually ring-shaped cake fried in fat
2 : something (as a mathematical torus) that resembles a doughnut especially in shape

— dough·nut·like \-ˌlīk\ adjective

Encarta Dictonary:

doughnut
	dough·nut [ dṓ nùt ] (plural dough·nuts) or do·nut [ dṓ nùt ] (plural do·nuts) noun