Both players made big progressions last year. Freese, after that big World Series in 2011, hit 20 homers (10 more than his previous career best), mostly because of a healthy amount of AB (501 in '12) and an uptick in HR/FB% (11.8% in '12, up from 8.4% in '11).
Alvarez proved that he's ALL power (30 HR and .467 SLG in 525 AB). But his batting eye is lacking. In at bats that started 0-1, Alvarez struck out 127 times. Once he's down in the count, he's unable to dig himself out of the hole.
I personally have Freese ranked higher than Alvarez. I feel both guys can duplicate what they did in '12, as none of their ratios are really that unsustainable. But Alvarez's strikeouts and BA kill you. I'm not a huge fan of players who act as balloons AND anchors.
Hope this helps.