The Wii U versions will sell exactly the same.

FF 13 begs to differ.

Im gonna go against the popular vote here and say Kingdom Hearts 3.

Final Fantasy as a brand has been hurt by the XIII saga, so Im tempted to think that XV will be automatically pushing lower numbers than the norm. If its good it will have great word of mouth, but I wouldnt be surprised to see it be a hit with the 2nd hand market.

Kingdom Hearts 3 will be hyped up to the back bollocks by both Square Enix and Disney. Thats the key thing here though. Disney's new found, overwhelming popularity with the mass market thanks to the acquisition of Marvel and Star Wars.

Star Wars and Marvel characters, along with the classic cast of characters we have had throughout the series will only help to push the title more with the mass market.

Kingdom Hearts 3 will be a 10 Million seller. Im calling it.

FFXV will dominate KH3. Only FFXIII can hurt FFXV sales.

Kingdom Hearts is a well established series, but sales wise it will not hold a candle to a mainline FF title.

FFXV will destroy KH3, both quality & sales wise!!!!!

Im confused by the idea of the KH fanbase growing since KH2. If anything many people may have left the franchise after 2 as there hasnt been a console game since 2005 and the sales of the HH games show that many fans of the series never showed up again after 2. Whos to say they are going to return 9 years later, many may not even game anymore or became a part of that CoD crowd like a few of my mates -_-

I'd say that Square screwing around with which console Kingdom Hearts has appeared on has hurt that fanbase far more than XIII hurt Final Fantasy's fanbase.

OT: Finaly Fantasy by a large margin.

I'd guess FFXV. It looks like a mammoth game production with a much more relatable story than the XIII series.

Personally I'm very excited for it and it will be a day 1 purchase for me.
Sure it has been in development hell for a long time, but that's not always a bad thing. In fact many of the greatest games spent an awfully long time in production.
But the FFXIII series has done a lot of damage to the franchise (even though they are still very good games imho), so I guess it will depend on how well it plays and how well the press will respond to it.

Kids games tend to sell more, so probably KHIII.