What is this games best comparison? Deciding between this and FF12
Open world single-player Monster Hunter with DMC-lite combat.
Really its difficult to compare since its the most Dungeons and Dragons based game ever. I've seen people claim it has elements of Dark Souls, Skyrim, DMC, Monster Hunter and etc.
I've always called it Dungeons & Dragons crossed with a smattering of Devil May Cry. It's definitely the most D&D you'll find in an open-world Action-RPG.
The Skyrim comparison comes from it having a persistent open-world. Major events change up the world-state for the duration of your run. And while you have a critical path to follow (with non-obligatory side-quests), once you're unleashed upon the world, you can go and do pretty much whatever you want. (Though some content and locations are gated by story progression).
I don't think the Monster Hunter comparison really holds up to any scrutiny at all. It doesn't have nearly the same focus on monster hunting (for one), nor does it have the instanced sessions that series was always known for.
There's absolutely nothing of Dark Souls in Dragon's Dogma, outside the most superficial. They both have core (but very different) Action-RPG gameplay and both play out in Western-style high fantasy settings. Both of those bullet points could be said about a ton of different games, however. Dark Souls was all the rage when DD hit last gen, however, so it made for easy-to-click article headlines.
So, what do we have? We have a vaguely Skyrim-ish persistent open-world, with day/night cycles, NPC schedules, encounters and loot that repopulate within 3-7 in-game days, and one you can explore at your leisure or mostly ignore until the game's critical path takes you to the various locations it winds up taking you to.
We have a real-time Action-RPG combat system that has more in common with something like Bayonetta or Devil May Cry rather than those of the relatively shallow experiences we see in Elder Scrolls, Fallout, Witcher, and other, lesser titles of similar ilk.
We have critters as small as mice, rabbits, and snakes, scaling up to humanoids like bandits and orcs and goblins and various undead, all the way up to classic D&D staples such as cyclopes, chimeras, beholders (called gazers here), griffins, drakes, and full-blown dragons. Ever critter, crate, chest, and harvest node is fixed. There's no scaling of loot or creature levels.
We have nine character classes (called Vocations) with highly divergent, thoroughly implemented gameplay. We have the three starter Vocations, Fighter, Strider (archer with double-daggers), and Mage. We have their three Advanced Vocation equivalents (Warrior, Ranger, Sorcerer), and we have three player-only Hybrid Classes (Assassin, Mystic Knight, Magickal Archer). We have 200 XP levels to play with as far as building stats go, and few limits as to what Vocations we can pursue and when. You choose from one of the three starter Vocations and are locked in for your first 10 XP levels, at which point you can spend special points to unlock any or all of the others, and customize your character however you see fit. These same points are used to purchase active and passive skills (mostly) unique to that Vocation, which become available as you rank that Vocation up (different from XP levels). The game is not particularly difficult once you know what you're doing, have a few XP levels in you, and some decent gear. So all builds are ultimately viable.
The game's main conceit is that you create TWO characters. You play as the story relevant Arisen, which you create first thing after a tutorial that teaches you the ropes. Not long into the game, you recruit a phantom character called a Pawn, which is an AI-controlled party member-slash-companion, who directs you to an encampment near your home village, which serves as a sort of staging ground for Pawns. After a brief "exam" there, you're able to create your own Pawn, with the exact same magnificent character creator you used to create your Arisen. This Pawn is your permanent companion on your quest and has access to six of the nine Vocations I mentioned above. The three Hybrid Vocations are Arisen-only. You may hire up to two more Pawns to fill out your party of four. These Pawns can (and should) be Pawns created by other Arisens, that is to say, other player characters. If you're playing offline, you only have access to Capcom's awful RNG-derived offline Pawns. I do believe that if you "favourite" player-created Pawns, you will have access to them even offline, but unlike your own Pawn, hirelings cannot be equipped and do not level up. So you'd periodically have to go online in order to download "fresh copies" of these Pawns (assuming their creators are still playing the game). Or you can kill your Pawn, never resurrect him/her, and go totally solo, if you wish. Your choice.
The story is kind of half-baked and bland, ending only once it starts to finally become interesting. But ultimately, it's just a vehicle for your adventures, and gameplay is absolutely KING here. The exploration, leveling, looting, and combat are some of the best you'll likely to experience in a game of this style. They may have been better open worlds since DD, but there absolutely has not been better combat or class systems in this kind of game. IMHO.