Human is considered weak against Undead. This is why there is no fixed strategy in HM vs UD matchup.
Undead can go mass Fiend, mass Gargoyle, mass Destroyers or a combination of these with Abominations(which is more likely). Most popular these days is Fiend+Destro+Abo combo. Undead hero- Death Knight 1st, Lich King 2nd.
Human normally tries 2 counter UD strats rather than go 4 a paticular strat. And this is why HM strats differ with UD strats. The most accepted strat is 2 get Mountain king(MK) lvl5, Paladin(Pala) lvl4 and Blood Mage(BMG) and go RPG. That is, try 2 get these heroes 2 these high levels as fast as possible(Except BMG. Only banish abilty of his is required). Sometimes Paladin is taken as 1st hero and sometimes Arch Mage is taken as 1st. In AM case, RPG is not as important as MK5,Pala4,BMG.
Air is normally countered with MASS Flying machines. Lots of them. Fiends are taken down by Knights. But the interesting thing is, when UD goes mass pierce+magic attack, Tanks(Siege Engines) can b used as they take less damage(only 35%) against those attacks.
This is probably the 1st match Mk5,Pala4,BMG was used.
In HM vs UD, nothing is fixed, and using wits is just as important as using strats.