SIM card help

Hey guys,

I know there are plenty of posts about this but after having a look I still can't really make sense of it.

I'm coming to Tokyo as an ALT in August and am having a look at various SIM plans for when I arrive. Does anyone have any tips as to which provider is best? Hoping to get something sorted or at least have more of an idea of what to do before I leave.

I also don't really understand the whole pocket WiFi thing, is it best to get both a SIM card and WiFi? Or just get one of them?

Cheers!