Choose yer poison
Relative to the Orcs, Humans have so many ways of playing a game it can boggle the mind. If you know where your opponent is, a nasty opening can be the Archmage rush. Set two or three peons to build your Altar, but otherwise keep your build the same. Get your Archmage out and running towards the enemy base as soon as possible, and put your point into Water Elemental. Summon one immediately and the second when you get inside the base. The opposing hero won't be out yet. With luck, the hero that's building is a one unable to cope well with the AM rush - like a Priestess of the Moon or Death Knight. Keep summoning elementals until you're out of mana.
Against Orcs, Undead or Humans it is very easy to force their peons off the production line. Night Elves aren't recommended as a target for the AM rush for two reasons. First, wisps can Detonate, causing severe damage to the elementals and draining the AM's mana. Second, most Night Elves open up with the Demon Hunter hero who will Mana Burn the Archmage and then kill him.
A more common opening is building Barracks and Altar at the same time, having an Archmage supported by Footmen. You can creep or harass with this force. Against an Orc or Night Elf player, it is worth considering researching Defend. Orcs will turtle with towers, but they have only 500 hitpoints and do only piercing damage. Night Elves often supplement their hero with Archers before switching to Huntresses. Massing Riflemen against Night Elves is recommended only with range upgrades and some Footmen to serve as meatshields. Once the Hunts close the gap, Riflemen tend to drop like flies.
No matter what, your first two heroes should be Archmage and Mountain King (usually in that order.) The Mountain King makes it risky for the enemy hero to engage in combat, since Storm Bolt does a buttload of damage and stuns. It is a great way to finish a hero off before he has the chance to Town Portal.
Orcs, being limited to Shamen, Witchdoctors and Headhunters for their anti-air, are very vulnerable to Gryphon Riders. Gryphons are similar to Wyverns but with their upgraded Storm Hammer weapon, they do bounce damage like a Huntress. While they're still not recommended for combat against support casters and anti-air units, the Storm Hammer makes them much more potent at it.
Gryphons are excellent against Tauren and any other units in Heavy armor. When assaulting an Orc base with Gryphons, focus on Burrows first since their 400 hitpoints and Normal armor are a joke. Be careful if you spot Beastiaries since that means either Wyverns or possibly Raiders with snares. The Far Seer hero is the only Orc hero who poses a threat to Gryphons, with his anti-air ability and Chain Lighting spell.
Other races, while not as vulnerable to the Gryphon Rider, are far from immune. Other Human players can suffer from Gryphon hangovers as well, since Riflemen are often skipped in favor of support casters. Scout Towers, like Burrows, have normal armor and fall easily. Once upgraded to Guard Towers however, they become much more difficult to take down. The Archmage is a Gryphon Rider's nightmare. Between Water Elementals and Blizzard, it is best to retreat when confronted with this hero.
Against Undead, Gryphons fare well since they are immune to Possession and Crypt Fiends aren't that common. Even if Crypt Friends cast Web on your Gryphons, it is easily dispelled by the Priest's dispel magic. We'd say Gryphons dominate Undead if not for the sturdy Undead Spirit Towers.
Night Elves have plenty of counters to the Gryphon. The always-popular Dryad, and the slightly-less-common Archer are potent anti-air weapons. The Druid of the Talon in Crow form isn't an economical deterrent but poses problems nontheless. Even Night Elf bases aren't the best targets for a Gryphon raid. Despite the general lack of static defenses in a NE base, there aren't too many vulnerable buildings or units. The gold mine is entangled and needs a lot of damage to break before you can get at the Wisps, so wood-harvesters remain your only easy target, but it's better to go after the Altar. The Keeper of the Grove and Priestess of the Moon are both capable of anti-air attacks, with the Priestess being the more formidable of the two. Once he has Starfall, it is suicide to attack her with the Gryphons.