It changes for me depending on what i'm working on for example i've just finished mastering a Metalica cover for a british band who landed a spot on a tribute cd.... the mix was in the style of 36 crazyfist's second record
So I had a good listen to that and got my ears all used to it.... then i did some work a/b'ing all the time then... then, cos the record is gonna be in the mainstreem I started to a/b to things like lost prophetts "start something" for level... noticed it was louder than the crazy fist record... so made a compromise on level between the two.
when i reconed it was finished i dithered it and put it down to 44/16.
after i'd done that i made a playlist in media player with loads of random stuff on it... today was tracks from, head automatica, motly crew, crazyfists, kill switch, crystal meth and alter bridge (yeah random i know)
and swaped my track around listening to the end of the last one and the begining of mine...the end of mine and the begining of the next one.... loud and quiet.... full range, just ns10's and pc speakers (to emulate a crappy kitchen stereo) (my mackie big knob is AWESOME for this)
and then made a couple of amendments. so yeah anyways thats what i use to reference.... not cd's, but wave files in playlists (NOTE not mp3's...Wave files)
Hope that helps mate,
C