I think a lot depends on the gameplan (big assumption there with the Mad Dingo at the helm). Do you want:
1. Fullbacks as wingers - Mogg, Folau etc to cover the high ball
2. Finishers - Speight (ineligible), Tomane, Mafi, Shipperly etc - pin the ears back and go for the corner
3. Crashball wingers - Ioane, Mitchell (when uninjured) to use in close as a decoy or alternative for a forward runner near the ruck
Of course, some have more than one skillset. Mitchell (at his prime) was both a finisher and a crashball winger.
If you play wide, then you want finishers, if you play a tighter game you want crashballers and if you are playing defensively and for the counter-attack (I suspect this is where Dingo is heading as the most conservative option) then fullbacks on the wing. I think a mix is best unless you have a one-dimensional gameplan (Dingo*).
And of course, it depends on what fullback you use - a defensive fullback (Burke, Morahan maybe), a counter-attacker (Mogg) or a playmaker fullback (JOC (James O'Connor) or Barnes). Again these categories are fluid and will depend on the other backs. Playmakers at 10, 12 and 15 is probably overkill.
I am still ambivalent about Cooper, but he seems the best option if he handles the pressure better than at the RWC. I like a crash-ball winger and a finisher or fullback on the wings and Mogg has some defensive weakness but I can't go past a long kicker at fullback, plus his counter-attack ability:
9 Genia
10 Cooper
11 Ioane
12 Lealiifano or Tapuai
13 AAC (Adam Ashley-Cooper)
14 Folau
15 Mogg
20 White (please not Phipps or McKibben)
21 Tapuai or Lealiifano
22 JOC (James O'Connor)
I know Ioane and possibly Folau are leaving but lets thrash the Lions then worry about future development prospects on the end of year tour.
* Does a vague "play what is in front of you" count as a gameplan?