Mage will provide you with a more interesting background and of course with a different playstyle. Mages are versatile, you can be a support and crowd controll focused long range supporter, a elemental damage dealer or even a close quarters combat mage or a hybrid. But you are a squishy little thing until you get some gear and skills that make up for the class armor restrictions. That is usually till several dozens of hours into the game and requires additional time investment. You also are restricted to elemental damage which comes with the natural tactical elemets in an RPG, like for example enemies natural resistances and immunities.
You like lots of flashy effects, pew pew lasers, the more tactical type of gameplay and above all: the feeling of wielding forces beyond human comprehension or ability? Then the mage might just be your cup of tea.
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As a warrior you can not focus on longe range but you are restricted to a melee role, however wether you choose to be a tank or a dps is yours. You are focused on dealing physical damage in large chunks, crowd controlling smaller enemies and building and destroying guard - essentialy a strong and important hp buffer mechanic. You can of course branch out into reaver to give your character a "sarcrifice hp for increased dmg" nieche, but do not disregard the offensive and control capabilities of the templar. Both specialisations are great but do not necessarily offer skills and bonuses you want to use in every encounter.
If you have ever wanted to be clad in the finest sheetmetal the scrapyards of thedas have to offer and wield large chunks of iron (or hide behind them, whatever you pansy) and love to get hit in the head by monsters at least twice your size, slowly turning from hungry skeleton to a human wrecking ball that bullies frost giants for their lunch money? Then warrior it is.