Right about now (Jan 28, 2016, 08:12 UTC), a Boeing 737-8AS is cruising over Manitoba/Nunavut on a delivery flight from Seattle Boeing Field (BFI) to Dublin Airport (DUB). The flight is labelled RYR800F, and is clearly a delivery flight for the European low-cost airline Ryanair.
I have always wondered who flies the plane in such situations. I would appreciate if you could give me a few insights into how these events are managed by the manufacturer and the Company. I envision the following cases, but which one of them, or combination of them, is true?
1) The plane is flown by a special pilot unit of the buying Company, which flies to the manufacturer's logistic airport, checks for conformity, signs a few documents, and then flies the plane to the Company's headquarters or hub;
2) The plane is flown by a special pilot unit of the manufacturer. They fly the plane to the Company's headquarters or hub, then meet the buyer to check for conformity and sign the documents. Eventually, the pilot unit flies back to manufacturer's base as regular passengers onboard other flights;
3) The plane is flown by two units: one belongs to the manufacturer and the other to the buyer. They check for conformity, sign the documents, and jointly fly the plane, in order for the manufacturer and the buyer to share immediate feedback on the plane's performance while airborne;
4) The plane is flown by a contracted pilot unit, which performs the duty as a third party payed by the buyer or by both the buyer and the manufacturer. This unit also includes a member of the buyer. They reach the manufacturer's base, the buyer's employee signs the documents, and then the plane is flown to the Company's headquarters or hub.
I assume each Company has its own policy in this regard, but which one of these procedures do you think is the most common? Thanks!

When an aircraft has to be delivered, who flies it to the destination airport?how was thatmainly about ferry flights for aircraft that are bound for logistic airports? – Federico Jan 28 '16 at 09:24