I traded Oz options for over five years and just in the last couple of months have shifted my trading to the US.
The reason for moving my trading is a combination of a few factors. The fees (not only broker fees but ASX charging $1.12 for every option contract traded) were eating too much into profits. Also Oz data is expensive. Trading spreads was cumbersome where the mid price had to be worked out manually.
What really tipped me over the edge was the Oz MMs refusing to quote or respond to quote requests during some high volatility near January expiry - even on BHP which I was trading at the time. I heard they were fined, but apparently no guarantees that it won't happen again.
Another difficulty with Oz options is that the MMs can take up to the first hour before quoting. Nothing... not even wide spreads. On the occasions I requested a quote early in trading- usually no response ...
Totally agree with xtanda that the night time trading is the worst thing. Hadn't thought about the forex rate being a problem at tax time - will have to find out more about that one.
I really like the ThinkorSwim software for US trading - it all comes free and they are constantly adding to it. The last release has added a back testing facility which is pretty cool. The features are too numerous to list here and the only way is to go through their tutorials. You can demo their software with a paper trading account (I believe without funding a live account) to get a feel for it.
http://www.thinkorswim.com/tos/client/index.jsp
I understand their fees can be negotiable and have heard that they will match other brokerages. I was able to get the ticket charge removed at this stage. They also give a lot of free education and have found their support excellent. Anyway, FWIW, that's my experience so far... but then the last broker I really liked just went bust