Netflix I like because it's user friendly, streams at a higher quality and (based on the US) will update content fairly often. I do prefer the US version though and will switch my iPad back soon. Will probably get appletv so I can have access to both.
iinet (inc. internode) is unmetered with Netflix.
One of the awesome things about Netflix (not for me cos no kids) is their kids section. It's incredibly easy for kids to navigate without stumbling on anything inappropriate.
Stan seems ok so far - same quality as netflix, though I'm finding it a little temperamental. It's content is similar, but a little different. More TV shows, less movies.
Presto I'm not impressed with. I have a six month free trial. It will only steam in SD. The only positive is that it has a massive range of older kids movies, particularly Disney. TV shows are an awful selection though.
With Stan and Netflix - it's $20-ish a month - so I figure it's less than buying a new movie a month. Unlimited internet so that doesn't bother me.