They will both kill you
From experience, I can tell you that Meth is not as intense as coke. As in, you don't get that rush like you get when you choke back a fucking honker. However, Meth is much easier to do for days and days when you chase the dragon cause your nose doesn't close up like it does on coke. Mine anyway.
As far as crystalizing in your blood, I have never heard that.