Agree with Satoshis, but for a somewhat different reason.  With whole BTCs I know I'm dealing with whole coins.  With satoshis, I know I'm working from the right of the whole 8 decimal places.  mBTC feels like it falls somewhere in the middle to me.  calling the BTC rate .451 or whatever it is today is one thing, but doing that for the alts just feels more complicated than satoshis.