‘ise’ is the British spelling – used in UK, Australia and other English speaking countries which have had an influence of British English historically.
‘ize’ is the American spellings. It is in standard use in American English.
For us Indians, typically in professional communication, the preference is towards US English and hence we generally see ‘ize’ spellings, for example: organize, sympathize, prioritize etc.
In literary writing though, you would find a general preference for British spellings and hence, ‘ise’ is more common.
For all practical purposes in our day to day writing, either of ‘ise’ or ‘ize’ would work.