Hi Pass Filter vs Lo Shelf ?

Hi pass filter cuts off any frequency bellow the cut point (and according to the slope you choose, which determines how much dBs per octave sound drops in level bellow the cut point), while low shelf boosts/attenuate any frequency bellow specific frequency that you choose. Hi pass is much more noticeable, while with low shelf you can make subtle changes (but not as subtle as you can get with parametric eq).

edit:^^yeah, if you think about that relationship between gtrs vs bass, usually you pick hi pass filter. Generally, you want to choose a little gentler slope (like 12dB) or a little steeper one like 18dB, but no too step, so that cut sounds as natural as it can. With low shelf you can remove any remaining excessive bottom end, but I'd use bell for that. That said, I tend to use hi shelf on guitars (for adding some air) a lot more than low shelf ;)
 
low shelf cut:
lowshelf.jpg


Hi-pass filter:
hipasslowcut.jpg