I've heard it's different between java and bedrock. As a bedrock player, Playing on Op items means: you can not do much for most of the game, then start playing the game and still be able to win. Basic Items means: staying at your base/camping does not help you (except for poseidon, which has no ores/ ore blocks as far a I know), and you actually have to be playing the game. Normal items is a good in between, where games don't last too long but also don't end in less than 8 minutes.
Tl;dr : in terms of game length, it's basic, normal, then op (at least when I play)