CANNOT CHOOSE
-A country on the continent of Europe (the Colonizers)
-The US, Canada, Australia, New Zealand (where the colonizers went)
CANNOT CHOOSE A COUNTRY THAT WAS NEVER COLONIZED:
CANNOT CHOOSE: Liberia, Japan, Thailand, Bhutan and Iran. The area that became Liberia had British, Dutch and Portuguese trading posts, but after the U.S. started sending free blacks and former slaves to Liberia in 1820, the area was never snapped up by any European power. It officially became a country in 1847. Meanwhile, Japan, Thailand and Iran were powerful enough/had strong rulers/didn't enter into "sucker" treaties/and/or played Western powers off against each other to such a degree that they've been able to maintain independence all the way to the present day. Bhutan fought a war or two against the British, lost some territory and political influence, but kept itself autonomous throughout the colonial period.
ALSO CANNOT CHOOSE: Nepal, Tonga, China and Ethiopia. Tonga was apparently under the British aegis as a "protected state", had a British consul for seventy years and was part of the "British Western Pacific Territories" for fifty, but it was able to maintain its own indigenous monarchy all the way up to the present day; in other words, it never gave up its right to self-government. Nepal was never a British colony, and in fact fought a war to ensure autonomy from the British Empire; however, they had to cede a third of their country to do it, which is why they're in the "dubious" category.
Ethiopia was one of only two countries (along with Liberia) to survive the Scramble for Africa more or less intact, but finally fell to Italy in 1936 when Mussolini decided to create his 'New Roman Empire'. The British ejected the Italians in 1941, and the country regained full independence again in 1944. (Eight years isn't so bad; consider the Philippines, for example, who were under Spanish, American and Japanese rule from 1571-1945.) Finally, China was technically never a colony (except for Hong Kong and Macao), but got screwed in so many other different ways by various Western powers (plus the U.S.) that it's hard to label them as a perennially free country with a straight face.
ALSO CANNOT CHOOSE: : North Korea, South Korea, Mongolia. Back in the day when Korea was one country, it apparently did a decent job resisting the West, but a lousy job resisting Japan, which ruled them for 35 years. Meanwhile, Mongolia was essentially ruled by China throughout the colonial era, and like Korea, was geographically remote from other Western territories or centers of power. Both the Koreas and Mongolia were able to escape rule by the West, but only because they were totally (Mongolia) or partially (Korea) ruled by other powers during that time. I'm not sure if they should get credit for resisting imperialism, given that.