Safety line with a slider is by far the best IMO. Tree steps break, branches break, even ladders break. So the only sure way to keep yourself safe is using a lifeline. This doesn't help you much when you are setting up the stand initially, but once you have your stand location set I recommend using one.
I have made my own fall arresters and sliders, but there are some really good mechanical ones available now too. Not a valid vimeo URL
I know three guys that had bad falls from tree stands. All three happened either climbing up or during attachment of the safety harness. Two were using ladder stands!! A sliding arrester would likely have saved each from serious injury.
