Buxton hit an unimpressive .248 in Rookie League. They are looking at things we don't see.
Sano hit .258 last year, also underwhelming. Again, they are seeing things we aren't.
I'm not saying they are right about everything. Just that they are seeing a lot more than we are.
Even when we watch the same game.
I'm not to worried about Sanos batting average, he had one of the top OPS seasons in recent history for a teen at that level.
One thing to keep in mind about prospects, no matter their "ceiling" or their tools, is that it will take some time to see exactly how good they will turn out to be. Cuddyer took about 3 years into his major league career to finally "break out". Parmelee and Plouffe will get an opportunity to be regulars this year, but we really don't know how that will turn out. They may turn into big league backups, solid regulars, stars or they could even go down the Valencia path. I am pretty excited about the Twins minor league prospects, but a lot of that, for me, is that I think there is a lot of depth. Buxton and Sano could be stars, but even if they aren't, there a lot of good prospects in the system right now who could become good major leaguers.
Prospect Rankings should consider two things.
1. A player's upside- Here is where I would argue Buxton over Sano. Buxton has the potential to make an impact in way more areas of the game (Base-Running, Defense, Hitting) where as Sano's Tools are extreme power plus a very good arm. If one questions-Sano's ability to stay at 3rd where as expecting Buxton to remain in CF then the issue gets more complicated. I look at Sano as a Miggy/Stanton type potential hitter (Rare 80 Power). He's an awesome asset for the System. I look at Buxton's upside as higher (Andrew McCutchen/Matt Kemp). This seems to be the Baseball Prospectus/Fangraphs View.
2. The prospects ability to reach one's ceiling. I realize Sano is a safer bet here. This is why he's probably higher on most prospect boards. I remember being surprised when Keith Law said he would be hard pressed to see a case made for a prospect other then Sano. Buxton has a much greater risk of flaming out.
I would rank Buxton higher. I realize that one would need Brass Balls to do a trade of Sano's Probability for Buxton's potential. One could make a valid case either way. This seems to be a choice of scouting preference.