The $25 Early Access on itch is a one off payment to get the game and have access to all future updates and content one month behind the patreon. The patreon, has access to updates a month sooner as well as the development, art and poll posts but you only have access for while you remain subbed so is more of a long term support of the game.
The $3 tier is essentially the same as the itch purchase as the access is a month later then the $5 one however you still support more long term and get the dev posts. If you cancelled your patreon sub after getting the game you would need to resub for the next update to get that though and so on.