I'm mostly happy with the Australian set-up.
Notes: $100 (uncommon), $50, $20, $10, $5
Coins: $2, $1, 50c, 20c 10, 5c
We ditched 1c & 2c coins about 20 years ago - hopefully we'll ditch the 5c soon, too. I've always liked the idea of the American quarter, though. ATMs only dispense $20s & $50s; $5 notes are super-common, there are plenty of $10s, but you need to specifically ask at the bank for $100 notes - anyway, how often do you actually need one? Also, wouldn't it suck to lose one.
What baffles me about American notes is that they are all the same colour, and still made of paper. Polymer notes are the go. I like the idea of a Euro-style currency union for the Asia/Pacific, too. It would be cool to get foreign money from time to time. Other than NZ coins, that is - especially the gold coins, they're impossible to get rid of.
I'm semi glad the Kiwis changed their coin sizes.