Nice, being the origional and "correct" version of the word, is most commonly used, however, the
two other spellings are perfectly acceptable, though there are differences. Niice, more
intense than nice, and yet not so
intense as niiice, is often used when something is funny or cool, though not as cool as something that is awesome. Niiice, being the most intense, is only to be used when something exceeds the awesomeness of nice AND niice.