H+ is a theoretical ion, because its a free proton, which is WAYYYY too reactive and does not really exist for any appreciable time when it is in a environment with lots of mean water molecules waiting to collide with it.
therefore when acids dissociate in water, H+ is produced, but it quickly attaches itself to a water molecule forming H3O+.
but when writing reactions, it does not really matter whether u write H+ or H3O+, because for balancing purposes, you cancel the water on both sides of the equation:
H3O+ + OH- --> 2H2O
more or less the same as
H+ + OH- --> H2O
this is to say, the water molecule that the proton is attached to does not react or anything, but is a spectator molecule.