Tonga is one of my favorite countries. Since many years I was searching for the difference between the small and large lettering. Compared many coins but never saw a difference till recently (with thanks to freeze_coins) and then the difference is very clear. So all the coins I ever saw were with large lettering which means the small lettering is much scarcer. And here it is:
The large lettering, although the letters are nearer to each other, comprises 54 (large) beads, the small lettering comprises 51 (small) beads.



