I prefer Wordsmith.
Better features (other than cross platform), including two big ones:
-limited to 3 attempts per try. No longer able to just place letters wherever and hope it works. more of a challenge
-Player records. Win/Loss/Best word/etc. This gives you more incentive to win!
-up to 4 players per game
-better push notifications
EDIT: imex already said it..LOL.