For the sake of sales, I think Sony should buy it. Shemnue will sell best in Japan (e.g. Yakuza titles) and they have a decent user base there.
However, I think MS will buy convince Japan to buy it as part of the "win japan over" process.
Ihope Nintendo don't buy it since I dont think Nintendo's hardware can do Shenmue justice. Shenmue was one of the most visually impressive games I had ever played last gen.It was so far ahead of its time, even 4-5 years after it had been released I hadnt seen another title like it. IMO it could only be done right on one of the HD consoles.
If it is down to nothing else but money, MS will get it. If it is to do with sales and money to a lesser extent, then I think Sony will get it.
Ideally, I would like Sony to get it and have Quantic Dreams help Sega with the production of it. I can see things in Heavy Rain that are reminiscent of Shenmue :)