Sue, from an old caravanner from way back (owned my first van 38 years ago, and have had 4 different vans in that time) I will give you some good advice -
I have used both, and in my mind there is very little difference.
The scissor jack is more stable when only down a short distance, and not stable when down a long way.
The stabiliser jack is not stable when only down a short distance, but very good when down a long way.
Both have threads that require some form of dry lubrication that doesn't attract dust and dirt.
Both should be on all 4 corners of a van that size.
Hope that helps.
PK