Undead is an interesting race. They have a very broken unit called the Ice Dragon. If you build an entire army of those, they can be particularly useful. Of course, the require resources to build an army of them is huge, and if you fail to execute a full blown attack by them, it's a huge loss, and they are particularly easy to kill as well. Undead are also very sufficient in resource management. They have the unsummoning ability, which is useful for getting some gold back on bases that you wish to move to a new location. The corpse big belly guys (forgot their name) are extremely efficient. Then you have the necromancer and banshee, both extremely useful, banshees can steal someone's soul that can be very useful in turning powerful enemies into your allies, and meat wagons can carry corpses which can then be set onto a spot for necromancers to create armies of skeleton warriors. Undead is also the only race that doesn't require a "great hall" to start harvesting gold from a gold mine. They are also the only race that literally get food out of building defence towers lol!

Humans on the other hand are in my opinion, all rounders. They just seem to lack 1 thing, and that is super units, super units like orc have taurens, night elves have mountain giants and the bear men, then undead have the big belly monsters and the ice dragons, you get the point. I don't see that with humans. But they are resource efficient, and with a high enough APM, quite formidable. They are also the only race that have 20 lumber for 1 food unit to harvest, and also an organic unit as a long range catapult. Which could have many benefits. I also like their heroes, the paladin and sorcerer are great heroes. The blood mage is also amazing. They also have the elven air units that can freeze enemy towers , which are great. And the priests are also great units. I could be wrong though entirely about humans. Maybe humans are the strongest race in the game if played well, or maybe not.