Personally, I prefer option (3) offered by Cúnla:
Go mairimid inniu. Go gcruthaímid amárach. Le chéile.
The same option with inverted word order (Inniu go mairimid …) also sounds good, but I think it runs the risk of putting too much stress on ‘today’ and ‘tomorrow’ and could be taken to mean something “Today is for living. Let us not bother with creating until tomorrow”. At least, that’s my reading of it.