If we're doing Americanisms v Britishisms, I'll declare my preference for -ize over -ise. It just looks better to me. Probably because I grew up reading Puffins and Penguins and other followers of OED-type spelling. So when people say they want "British spellings" I know they mean -ise instead of -ize and I give them that – even though they're wrong!
AIUI both spellings are British. English was all
-ize until Dr. Sam'l Halitosis Johnson decided that such endings were of French origin, and since in French only
-ise is used we should use it in English too. So unless you're a Johnsonite,
-ize is correct except in words whose roots contain
ise or an ancestral form thereof, e.g.
excise from Latin
excidere, excisum to cut out.