standard="oversized". very bass heavy. good for the nu-metal chugga chugga chunk. think godsmack and that sorta huge sound where the bass hits your chest.
traditional=normal sized, as marshalls, etc. can still sound huge depending on your EQ, but the sound is definately tighter. perfect for thrash metal, speed metal, that sorta thing where quick articulation is necessary.
this is not to say some who plays one style only plays the specified cab, but these are the stereotypes and they hold true. if you got an already tight amp, you could be ok with standard. if you got a recto amp and think it's a already rather bass boomy, you may want the trd. look up your fav bands and see what they use in the studio, then reflect on what styles you'll play.