All things considered,_____ not a

bad day.

its or it's

"It's" is a contraction that is equivalent to "It is".

"Its" means "that which belongs to it", and is in the same category with "mine, his, hers and ours"

Which do you think fits in the blank?

Whenever you see an apostrophe "'" in English, it indicates either a contraction (as in "they're" or "can't") or a possessive form of a proper noun (like "Mary's handbag"). You do not use apostrophes for possessive pronouns (like "hers" and "its".