I'd definitely rather have Giles. Blalock is still really green, and Giles seems to have really improved himself. Keeper league, I might say something different, but for this year, I like Giles better.
Anyway, what's more important is what you need. Do you have Soriano? Well, then I guess you should pick up Blalock. These guys play two different positions, so they're not apples and apples.