My preference for nitrogen cylinders is Option 1. Nice and convenient to have a couple on hand at all times, and not over the top price. I already have the soda stream adapters which helps, but would still go option 1 and purchase the adapters to suit if I didn't. Like altone above, I always prefer reusable over throw away items and at under $60 to have a couple on hand (plus a regulator), it seems like a pretty reasonable entry point for anyone like me that's never run nitrogen.
Having said all that, I'm in QLD, so I'd need to make sure I could get them refilled locally.