I agree - can't see any reason why the A330neo isn't a viable option. There certainly seems to be a bias towards the 787-9 from some members here.
AR would probably need the range of the A338 and only six of these have been ordered so far overall (and by just one customer). As has been extensively discussed here on A.net, it seems very unlikely that anyone would provide decent financing for such a niche plane with extremely limited resale potential. Concerning the A339, the 251t variant might allow EZE-MAD without relevant restrictions but probably not FCO, at least not providing any improvement compared to the current A332. Financing prospects for the A339 would be better than for the A338, but hardly as good as for the 789, which would probably eat into the higher discount Airbus could offer for the A339.
AR first needs to replace their remaining two A343 (FPU and FPV) in 2019, then the four PW-powered A332 early next decade (FNI, FNJ, FNK, FNL), then their two ex-BR A332 (GKO, GKP) and finally the four A332 they got directly from Airbus in 2015 and 2016 (FVH, FVI, GHQ, GIF). Whether they choose the 789 or the A359, these will probably be deployed on the European routes first as that’s where the most significant efficiency improvement can be achieved and where the A332 operate much closer to their limits. Then the four newer A332 currently operating to Europe would be cascaded down to JFK, MIA and CUN enabling replacement of the older A332. I would expect the four newest A332 to stay with AR well into the next decade, but not operating to European destinations. In this somehow simplified analysis the A359 would have the advantage of commonality with the current widebody fleet until completing its replacement while the 787-9 would probably be cheaper to buy/lease, easier to fill and offer the additional advantage of two engine options and the possibility to complement it with the smaller 787-8 if there is a business case for it.