Pantheon: Builds Tanky dps or AD carry, he's strongly at early game when he can take you 2/3 of you life down with one combo, but he falls off late game. The fact that he can teleport its good, even better when a lane is getting ganked.
Mordekaiser: Builds Tanky or AP carry, Strong at every phase if played correctly (Morde solo top can wreck everything at early game). The thing that you can turn a 5 vs 5 into a 6 vs 4 its just epic (You ult the ad carry of them, kill him and BOOM, AD CARRY PET)
I am more of a pantheon kind of guy I suggest him mainly because I haven't really every had a problem with him and I have played with a few people who have used mordekaiser v. Pantheon and have seen Pantheon dominate throughout the game.
Ok^^ in fact i buy Pantheon^^ and his VERY GOOD i recommend it^^.
Pantheon is amazing, but i find his ult useless since it never seems to hit an enemy champion due to how long it takes
Ahh, this is true xD, his ult is for teleport but ult is excessively slow..
Morde.
It's sad to say that pantheon isn't that good late game atm.(even though he was one of the first champs i mained in lol)