Dragon, RX-505 or DR-2 ?

I have the chance to get one of the 3 decks mentioned. 

The Dragon works but the NAAC is slightly out of line, it’s an early serial number which I understand can mean an expensive service. The sales price is of course the highest!
The RX-505 works as expected, just never serviced and is being offered at half the price of the Dragon. 
The DR-2 is near mint and hardly used and is priced between the Dragon and the RX-505. 

Which one one would you choose?
I can only relate my experience. Although I don’t know the DR-2 I have owned the Dragon (that I bought from Willy Herman), and an RX-505 (serviced by Willy). Both machines worked flawlessly, and I still have the RX-505. I couldn’t hear much difference between the two, both were great. If you only plan to listen to commercially recorded tapes, I recommend the convenience of the RX-505. The previous poster is correct that the Dragon will likely be the most expensive one to have serviced. Any higher end Nakamichi is worth the cost of service or repair. You can still find used (and sometimes new) cassettes at thrift stores for almost nothing. If that RX-505 is the lowest priced deck, you may be in luck.
As an owner of a Dragon, I’d choose the Dragon. Regardless of which you choose, all of them will really need a complete rebuild to perform their best. Sure, they may work, but I promise you without a restoration they won’t perform to spec. 
The Dragon and RX-505 have the same transport, which was Nakamichi's best. The DR-2 was a somewhat cheaper design, although still better than most other brands of cassette decks. Sounds like the DR-2 may be priced a little high, but it would be my last choice regardless.
Congratulations! I would take nrenter’s advice and look into service. It’s worth the money.