It doesn't make a difference, in either case you'd need to get on a line to exchange your voucher (if purchased on line) or the artecard for an actual ticket.
we will get the card then, i think it will benefit us more
can i use the arte card for the train from sorrento to naples
Yes, you can use the 3-day Tutta la Regione card's transport pass for the train. You must have the actual card, however, not an on-line voucher, for the transport service. You can get this at the train station in Naples or at the airport.