I went to Castle Hill and passed first time there. It's not too hard provided you know the place pretty well (eg. the 25 zone, the stop signs, lots of roundabouts, etc...) and patience is very much needed when coming off onto Showground Road.
My sister did hers at Hornsby and also passed first time- with only 13 hours I think.
Btw, the difference between places I think is just the course/route and whilst there may be leniency or more areas to fail you on (eg. more stop signs or more round abouts)- if you're a good driver, it shouldn't really make a difference.
EDIT: I think the time slot you book it however does make a difference... it's definitely a lot easier when you don't have to worry about little kids/school kids running out onto the street and crazy parents rushing to drop off their kids and get to work. I personally did mine at 10:15am and the traffic was pretty good. The Castle Hill test wasn't too bad 'coz not that many cars so only had to wait a little while to turn out onto showground.