DISCLAIMER: This text was published on the Kickstarter campaign page for Battleground Fantasy Warfare: Men of Hawkshold as an update and I feel it is a good one to share (the authors agree and have given consent).
Faction Recommendations to New Players
When making recommendations for new players, I break the factions down into three categories, based on variety and learning curve. These are not power rankings, but rather what I would recommend to a new player to get them into Battleground.
Seal of Approval
Great factions that I would recommend any new player pick up.
Elves of Ravenwood: in my opinion, this is the best factions from a design standpoint. Great replayability thanks to its variety of units, awesome theming, an army ability that is the gold standard for how faction abilities should work (i.e. usually not as good as a card but sometimes better), an army-wide special rule that is both easy to implement in-game and make the faction feel different, and finally a unique set of Command Cards.
Get Elves of Ravenwood because in the beginning it'll be your gaming group's "skill faction" but over time you'll be able to try new things with it.
Orcs: If Ravenwood is gold then Orcs are the silver. A very fun faction with a ton of variety. It has more replayability than it first appears, because you can go small armies of just Orcs, mixed armies of Orcs & Goblins, or even an all Goblin swarm. You can win with your infantry busting through his line, or by outmaneuvering him, or you can even build a stand-and-shoot army with them! Its army ability ("Lash") is thematic and makes them actually quite good at exploiting break-throughs.
Get the Orcs because in the beginning they'll be your gaming group's "toughness faction" but over time you'll try different builds with it.
Men of Hawkshold: Woe to those who deride Hawkshold as "boring old humans." Its claim to fame is its flexibility. You can field a cavalry strike force, a line of infantry, a stand-and-shoot, or any combination of those. When it comes to replayability, Hawkshold is far and away the best.
Get the Men of Hawkshold because in the beginning they'll be the "standard humans" but over time you'll discover it is a flexible faction with an answer for every enemy and every situation.
Good factions, each with a definite play style.
Undead: An extremely forgiving faction because your units won't run, and the faction has an offensively-oriented slant. It has a very hammer-and-anvil approach, with Zombies pinning the enemy down while your major unit destroy the enemy, or it is a fragile army of brittle Skeletons and skittish Ghoul Packs.
Get the Undead if you like an army that really captures the theme of playing a necromancer.
Dwarves: A really powerful faction, with a great command card deck... but you'd better love playing Dwarves. They are the core of your army, whether you bring the fight to the enemy or stand back & shoot. That said, nobody is better at outlasting an enemy than the Dwarves.
Get this faction if you love the Dwarven playstyle: win by grinding the enemy down.
Lizardmen: The "Power & Toughness" faction in that its strong & tough. Because of its army-wide special rule (they get braver and get more attack dice if fighting a beat-up opponent) I call them a "downhill army" in that they pick up momentum. They also have some of the cool units like the Tyrannosaurus Rex, Raptors, Triceratops Herds that add flavor to your game.
Get the Lizardmen if you want to introduce unique units to your play group.
For Something Different
These factions have a lot of variety and fun special rules, but that comes with a higher learning curve.
Umenzi Tribesmen: thematically this faction has a unique archetype. Its playstyle is essentially a synergy of light infantry horde, short range shooting, and support magic. Oh, and a Giant War Elephant… However getting those different components to work together can be a challenge and being mostly infantry means you lack the ability to redeploy. Playing Umenzi requires you to think differently because they play differently than most factions.
Consider the Umenzi if your group is ready for a faction that is unique in both theme and play style.
High Elves: Strongest. Faction. In the Game. The combination of high skill, selective access to high Power, one of the best tank units in the game, and the best combination of faction abilities (Maneuver Mastery & Sprint), the High Elves almost have it all. Plus they have decent replayability because of the variety of Core units. The catch is they are brutally unforgiving because of the fragility of your line and you really have to know to maneuver. You can't simply line up and charge with them, like Dwarves or even Ravenwood.
Consider the High Elves if you are ready for the challenging army where your victories seem effortless but your defeats can be total.
Monsters & Mercenaries: Despite being a "mercenary" faction, Monsters & Mercenaries actually play pretty well on it's own, but they are unforgiving. Many of your units are Stupid or are always on Close. Although many of your builds are going to be some variation on "4 Core choices and HULK SMASH!!" you do have quite a few things with which to smash.
Consider Monsters & Mercenaries for a faction that is pure fun & more powerful than you'd first think.
Dark Elves: Probably the second best faction in the game, because of the wide variety of units it can field. Only Hawkshold and Ravenwood have greater variety. And the Dark Elves have tons of special units with really cool rules. The catch is those units have greater complexity and you may be so spoiled for choices that getting them all to work together is a challenge.
Consider the Dark Elves if you want a magic-heavy faction with a large variety of units.
Wuxing: An army of magically animated terracotta statues and other elements of Chinese fantasy isn't something you see every day. Monks with different fighting styles, rocket arrow batteries, jade dragons, the Wuxing is loaded with all different types of units with thematic special rules. The catch with special rules is keeping them all straight and coordinating the disparate elements of your army into one cohesive whole.
Consider the Wuxing if you want a highly thematic army requiring subtle mastery.
Rome: Rome conquered the world, so you should be able to set up three lines and steamroll any enemy, right? You'll find out how quickly that doesn't work (and didn't work when they faced Hannibal). Rome is a solid army that grinds its way to victory in a unique way. However, like all Historical factions, they have a learning curve when it comes to their rules.
Consider Rome if you want to grindy playstyle, like Dwarves, but with a twist.
Carthage: On the surface they look very similar to Rome, but in truth they are a finesse army of very specialized units. This specialization gives a variety of playstyles and the ability to have an answer for most enemies. But like all finesse armies they are unforgiving and the Historical rules do have a learning curve.
Consider Carthage if you're ready for a finesse army of humans.
Alexander: This is an army of extremes, with most of units being "hard-hitting but fragile" or "tough but ponderous" and it will test your skill as a general. Despite the possibility to field a surprising variety of builds and having some very strong abilities this faction requires both skill and confidence to ride the razor's edge to victory.
Consider Alexander if you're up to the task of combining the disparate warriors of Ancient Greece and Macedonia into the best hammer- and-anvil Historical faction.
Persia: At first you'll think Persia has a wide variety of units (it does). Then you'll think that getting all those units to work together is a real challenge (it is). Finally, you'll understand that Persia, when used correctly, is a faction that is greater than the sum of its parts.
Consider Persia if you feel up to the challenge of forging a thousand nations into a single indomitable force.