I find it better to use air for thoracic epidurals and saline for lumbar epidurals.
I use continuous LOR technique, I find early loss of fluid occurring with the saline technique as you are pushing especially elderly people with lax tissue.

Therefore I prefer saline technique in young( mostly needing labour analgesia)
In thoracic epidural with slightest appearance of fluid I do not want to proceed any further, all these make me prefer saline technique for Thoracic epidurals and saline for lumbar epidurals.
thanks