I prefer American spelling in principle. Its introduction was carried out with extreme moderation (think of all the unnecessary simplifications in Chinese) and is very logical. The ending -ize rather than -ise reflects the Greek and Latin roots of such words; colour didn't really succeed in carrying the torch for the French couleur, whereas color returns to Latin and is identical to Spanish and no further from our pronunciation; gray from grey looks like day and may as it should...
It's just that I grew up with Canadian spelling (British + jail and tire about sums it up) so I usually write that way. To do otherwise would take a political decision, which I'm not prepared to do at this point. Canada rocks, and the US .... doesn't ;)
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