Many consider the main roles as the most important factor when deciding what to do with a hero, but that's just a general indication of what to expect. Sure, when you see Mage or Warmage or anything like that, you know already that you're talking about a damage dealing hero with tons of mana. But the skills vary from hero to hero and you have to keep them in mind at all times. Even more, you must make sure that they are useful for your particular team setup. For example, Silent Blade (screenshot above) is a really good Green hero with an apparently amazing Commander Skill: +30% Attack and max HP to its allies, plus other bonuses. The problem is that this only applies to other Green Heroes - so if he's the only Green one in your team or you only have one other Green Hero in your setup, the benefits you're getting are not as great. But Commander Skills are not all: you have to consider all the other skills (mainly the Special Skill which is basically their special attack that you trigger when they have enough mana) and the Passive Skill. And here you have just as many options as heroes exist. Try to find a balance here: while it's usually a good call to focus on choosing heroes that can really pack a punch and destroy opponents easily, you shouldn't ignore the power of support-type skills.