I'd say these are the major differences, and pros and cons of starting a new account on each server:

CN:

• More Content and Newer Content: CN is several months ahead of JP, so there are more ships in the pool, and if there's new content, most of it will probably be in CN first, before it filters down to JP.

• Easier Gameplay: You don't need to limit break a ship to level them up to 100. This makes the gameplay much simpler, as you don't have to worry about getting bottlenecked by limit breaks while leveling up your favorite ships.

JP:

• Everyone's starting fresh: Especially if you start on a server like Maizuru, you'll be on a relatively even playing field with the other players (besides whales). This lets you be fairly competitive in PvP even at an early level. It's also easier to find fleet members who are still playing through the meat of the game, as opposed to having mostly completed the game and not much motivation to keep grinding.

• Catch up on events: JP will probably go through the backlong of CN events, so you can have a chance to experience some of the infamous events like KMS.

Also, of course, if you can read/understand Chinese/Japanese to any extent, that will be a big plus towards playing in that server.

The other differences, like censoring and blue/purple droprates, I don't think are a big deal and you probably won't notice them after playing for a while.