I didn't grab the data book so my details are a bit off but the
     general idea should be correct.

     Both the HC04 and the LS04 perform the same function (inverters I
     think).

     For the inputs:
        HC inputs draw only a few microamps, LS draw a lot more current
        HC inputs look more capacitive than LS inputs
        HC thresholds are at (I think) about 1 Volt and 4 Volts
        LS thresholds are at (I think) about 1.8 V and 2.4 Volts
        (The point is: HC needs nearly rail-to-rail driving to work)

     For the outputs:
        HC swings nearly rail to rail, LS pulls low okay but can't pull
     high well
        HC can source and sink around 20mA (about).
        LS can sink 20 mA but it can only source about 5 mA


     For the gates over-all:
        HC is very ESD sensitive - in circuit and out of circuit, it will
     'latch up' in circuit and fry.
        LS is a power hog but it's hardy.
        HC designs usually have 'richer' frequency content - so if RF
     emissions are a problem go with LS if you can.



     I'll probably think of other things...

     I hope this helps.

     Jon Bertrand
     jonb@cirris.com