Corien: Warmachine and Hordes are companion games, both produced by Privateer press. They share the same setting, and the rules are compatible, such that you can play a game of your war machine faction vs. your opponents hordes faction.
The primary difference is in how magical energy resources are handled. Warmachine works via resource allocation. In warmachine, your general is a 'warcaster', and warcasters generate their own pool of energy each game turn. They then distribute this energy between their various robots or 'warjacks'. The warjacks use this energy to take extra actions like run, or charge, or make multiple attacks, etc. Energy not distributed to jacks is kept by the caster, and can be used to enhance their own personal offense or defense, or to cast spells. Apart from warcasters and warjacks, you also have units and individual non-caster models or 'solos' that act on their own and do not use energy directly (although they might be buffed by spells that the warcaster spends their own energy on, etc).
This means that you have to find a balance between using lots of warjacks and saving your caster's energy for magic or just personal butt kicking. Since infantry doesn't use energy, it's often the more effective choice for the bulk of your forces, though what works best will vary from caster to caster. Also, as the game progresses and you start to lose warjacks, your caster tends to become more powerful, as they're not spreading their resources as far.
Hordes flips the Warmachine resource model on its head. Instead of a warjacks, you have monsters or 'warbeasts'. These do not use up energy from the caster to perform strenuous actions or activate abilities, instead doing so generates 'rage'. The caster then leeches the rage off of the warbeasts to buff themselves or cast spells. The amount they can leech each turn is limited by their magic stat, and any warbeasts left with rage on them after the leeching is done has a chance of going uncontrolled and potentially attacking your own models. As a result, hordes is less resource allocation and more resource management.
Honestly, I prefer the hordes system. The result tends to be more dynamic play, and the big monsters, the centerpieces of the game conceptually, are far more central to how it functions, where as in warmachine the actual jacks can sometimes feel like a drain on resources. On the other hand, Hordes can suffer more form a death spiral, where attrition results in one side effectively losing the game well before its actually over, where as in hordes your caster remains at full strength until dead, and victory can be snatched from the jaws of defeat right up until the end. Not that last minute turnarounds can't happen in hordes, just that once you've lost your beasts your warlock has a lot less capacity to pull it off.
Regardless of your faction/resource preference, 'WarmaHordes' is quite a fun game. It is cheaper than warhammer or 40k, but not because the models are any cheaper. They cost just as much, or more, per model, and the model quality isn't at the same level, so model wise you're paying as much or more for a lower quality product. However, the game is skirmish based, and as such tends to involve a lot fewer models on the table. A largish game of warmahordes might involve about as many models as, say, a 500 point game of 40k, and fewer than a 500 point game of fantasy. Models move and act individually - even those in units (though they have to take the same actions and stay more or less in coherency), so you can expect a game to take longer than a game with the same number of models would take in a GW game, but average game length is still shorter since, again, fewer models on average, and the game turns tend to be a bit faster paced.
Balance is pretty decent between factions, but can sometimes be a bit wonky when playing a warmachine faction against a hordes faction (for instance, a number of warmachine figures have special rules for fighting warjacks which would have no affect against warbeasts). The game community does tend to have a solidly power-gaming mentality. Theme lists exist and its common enough to see them played, but you can expect your opponents to exploit cheesy combos and powerful units and characters for all they're worth. WAAC gaming is the default play style in that game, and the rulebooks themselves make that clear, so you should know that going in.
Warmachine factions:
Cryx - an necromantic pirate nation ruled by evil father of dragonkind in the setting. He was betrayed by his draconic offspring in the past, and as such no longer creates progeny, so don't expect actual draconic units or models. Their leaders are steampunk liches and
pirate queens, their soldiers include zombie pirates, wight warriors, and a few living troops, including corrupted ogres and trolls, and a subfaction of all female blood magic using amazon pirates. Their warjacks tend to be fast but somewhat fragile. As a faction, Cryx is known for being tricksy, with a lot of obscure special rules and warcasters with abusive spells. Probably my favorite faction, even if I prefer the game mechanics in Hordes.
Menoth - religious crusaders / zealots drawing inspiration from early christian and islamic themes. Expect elite crusading templars (with shoulder pads that would put space marine terminators to shame - some are more shoulder than man, now), skirmishing warriors lobbing grenades, and melee leaning jacks with balanced offensive and defensive stats.
Cygnar - more or less the 'good guys' of the setting - though their previous ruler was a despot and many still dislike them. Technological innovators, with guns, and weapons powered by magical lightning, and a bit more of a ranged leaning than other factions in general.
Khador - hailing from a nation of bitter cold, Khador draws inspiration from soviet russia, with big, heavy, bright red warjacks and armor and so on. Slow and heavy, with a melee focus and powerful armor.
Retribution - The elf faction. I don't know, they're in decline or something, like elves always are in every setting. Lots of magic, shooting, stealthy business. Some 'elegant' warjacks. You know the drill, they're elves.
Convergence - a new clockwork faction. I haven't seen their rules, but their stuff looks awesome. Basically a collective of spellcasters who decided the best path to immortality was to transfer their consciousness into clockwork bodies. Super cool look. Just released a few months ago, though we've heard about them in the fluff for a while. One of their number famously
defected to Cryx.
Mercenary factions - there's some cool mercenary factions, originally intended to be hired as allies by other factions, but they can be run on their own. Expect fewer options if you do, but can be very cool and flavorful. Dwarf bankers, disaffected deserters, and regular pirates (as opposed to undead pirates, ogre pirates, or horned, warrior women pirates, which can all be found in Cryx) can be found here.
-----------------------
Hordes Factions:
Legion of Everblight - a faction of elves and ogres that have been corrupted and dominated by a dragon. This dragon actually splits its body into small pieces used to create the blind, draconic warbeasts the faction uses, so if you want to actually play with a dragon theme, as opposed to an undead theme with a dragon ruling in the background fluff, then the Legion is the faction for you. Extreme emphasis on speed and offensive punch - both melee and ranged. Legion tends to kill fast or lose, and will crumple in attrition battles. Some very cool models. These are the ninjas to oppose the pirates seen elsewhere in the setting.
Trollbloods - blue skinned scottish trolls. more or less the good guy faction of Hordes, though they do have a grudge against Cygnar, the good guy faction of Warmachine, due to the latter killing them and stealing their lands under the previous ruler, and continuing to look down on them now. Think british/scottish sort of thing. Tough in general, with hearty, punchy warbeasts that are basically just bigger versions of their regular guys. These are the big bruisers of Hordes, roughly analogous to Khador in Warmachine.
Skorne - an original fantasy race hailing from a harsh desert, currently ruled by Cygnar's former despotic ruler. One might think of them as blood elves, with a bit of a shogunate theme aesthetically, though they aren't actually elves in the setting. These guys use necromanticy, but rather than animate the dead, they use it to enhance their magical powers. They draw strength from pain and torture, and have powerful, elephantish warbeasts.
Circle Orboros - team druid, with druidic casters and rangeresque units. Their warbeasts included werewolves, forest creaturs, and animated golumns created from living wood and enchanted stone.
Minions - These are the mercenary factions in Hordes, though generally with even fewer options and attention from designers than their warmachine counterparts. The most notable of such are, iirc, team alligator and team warthog.
More information about the games can, of course, be found on
privateer press's web site, along with discussion forums for the games and their factions.
