I think you would probably do ok with either - there is only a 4% difference in overall lengths.  I am 6'1" 175 and have been riding on center mounted 171s for two seasons.  I will probably go to 178s next time I buy them, but really just for an extra bit of stability on jumps and pipe.  For jibbing, I think the 171 makes it a little easier to ollie onto stuff.