the heavy lance stab outreaches the great lance. in my opinion the latter is a support weapon for 1h cav only, a great one however.
as the stats are atm, you should consider the heavy lance if you must attack 2h heroes head on or do fast hits on plane maps as the speed bonus is usefull with it. in any other situation, the lance is the better choice.
wall of text why the lance outclasses the heavy atm and in the right hands:
even in a head on lancer duel, the lance wins over the heavy lance, as a skilled vanilla lancer can outmaneuver the slow stab animation of the heavy lance and then close in and strike with his considerably faster lance whilst the heavy lance is steal in its stab animation, making a block impossible. (the aformentioned scenario accures in low speed encounters which happen when two apponents know of the others strength and enter this reaching game, its not the usual encounter but kind of a "duel" situation. this slow encounter also disfavors the heavy lances, whos' damage is greatly dependent on speed bonus.) this however only goes for master level cavs, so you want to consider it if you should want to stick to lancing and think current lance stats will be arround for a while.
even the light lance can be a viable choice if you want to do lots of backstabbing and off-horse hopliting like mentioned above
happy new year btw,