I'd like to add an extremely important factor here — that only SideFX seems to provide — and that is world-class customer support. We are so used to what Autodesk and Maxon and Adobe call "customer support", that what SideFX do here seems almost like fantasy, but is actually real.
For starters, they put out daily builds that contain bug fixes and even new features on occasion. Anyone can download these daily builds (even the free Apprentice users).
If you submit a showstopping, high-priority bug report, they will address it with urgency and put out a bug fix at astonishing speed.
You can send them your scene file to analyse, and they will actually analyse it and get back to you with a surprisingly quick turnaround.
Their customer support staff are well-trained and actually competent, and you will frequently get direct responses from the developers, even for minor reports.
The forums are also frequented by developers, and by helpful industry veterans, so you will almost always get a useful, helpful response to even tricky questions.
I am not a SideFX shill, and will criticise them where applicable, but I can tell you wholeheartedly - the support you get from them is on an entirely other level from everyone else out there, and that adds a tremendous amount of value to a production.