Alexei: 28 years old in coming season
Starlin: 21 years old in coming season
So, Alexei is pretty much at his peak right now, while Castro has 7 years before his peak should start.
AVG (I know it is overrated):
Alexei: .282 last season
Castro: .300 last season
Again, at age 28, Alexei will get better IMO, but he will be declining before Castro's prime even starts.
Fielding:
Alexei is much higher, and was an above average fielder this year (and way above average) for the second straight year (a little above average in 09, way below in 08) (via UZR/150), but Castro was seen as a stellar defender throughout the minors, so it is too early to judge, after all, as Alexei made the bounce back, at Castro was only a -2.1 UZR and -3.0 UZR/150, not terrible in that category.
Additionally, using The Baseball Cube's formulas that result in a rating out of 100 in each category, Castro matches up better than Alexei.
POW: Alexei 44, Starlin 41, (this takes more than HR into consideration, but I'm not sure about his one right now).
BAT: Alexei 70, Starlin 88,
SPD: Alexei 70, Starlin 75,
CON: Alexei 82, Starlin 84,
PAT: Alexei 19, Starlin 20,
Of course, that is just a scouting report.
And I know Alexei is better now, but I don't see how you don't think a 21 year old Castro has a better future than a 28 year old Ramirez.
I like Alexei as much as the next guy, but still...
I'm not trying to start a fight in the Sox forum, just explaining as asked.
Come on Brett, you've met this kid even
.
I don't think this is even debatable, which is why I only showed certain stats and one scouting report. And again, I said future.