One of my favorites is probably Treant Protector.
He is a kind of universal hero. He's great support with his Nature's guise and Living Armor, awesome tank because of very high strength grow and Living armor, and even, in some cases, decent carry, because his base attack is the HIGHEST in the game.
He can fill almost any lane role, but I adore going mid with Treant. Reason is his incredible base damage and living armor. With quelling blade you will hit creeps for almost 120 damage at lvl 1, which means that with half-decent last-hit skill you will just straight kill and deny every single creep. With living armor you will be just immune to almost all forms of lane harassment. But Treant is not the ultimate mid hero, however. He gets destroyed on mid by half decent Outworld Destroyer, Templar Assassin or Batrider. Also, Treant does not "WIN" mid, as it is actually hard to kill a fleeing opponent. What I do on mid, is I try to outfarm my opponent, get lvl 6, get arcane boots and just go ganking! With Invisibility, cheap ass ultimate and slow you'll be an incredible team asset.
Now, for skills.
Nature's guise is take one early, but max last skill. It gives you or your ally hero an invisibility and increased movement speed for some time, but only as long as they stay near trees. So, it is kind of situational invisibility. Use it creatively. Also, Treant can cast spells in Nature's guise without breaking invisibility.
Leech Seed is take one early and max second skill. It is mainly used for chases, pushes, and assists in team fights, because healing 300 hp to everyone in a range is kind of awesome.
Living Armor, is take first and max first skill (at least for me). This is one of the most powerful early game spells in my opinion. With 25 mana cost, 195 total heal, block of 80 damage for 7 instances and GLOBAL RANGE, Nature's guise is the skill that cannot be overestimated. You have to have good map awareness to use Armor for full extend. Look around the map, and cast the spell on any hero that needs some heal or who is being actively chased. I cannot count how many times I saved allies by armoring them when final blow was already flying in their direction.
Overgrowth, on the other hand, is a little bit underestimated by some players. It is not even a proper disable, it just prevents enemies from attacking and moving for considerable amount of time, but they can still cast spells and there are ways to break overgrowth. However, the main advantage of Overgrowth is its range, almost instant cast time, and, the most important, very little cooldown that allows to just cast it on one fleeing enemy hero. Also, enemies caught in Overgrowth cannot go invisible (if they were invisible when you casted it, they won't be affected), cannot blink (but Magnus can use his skewer), and it affects magic immune heroes (but if they activate magic immunity during Overgrowth they will break it).
So... yeah, that's Treant Protector for you.
But, generally, you shouldn't ask for advices for specific heroes. Just play all of them first and then figure who you like more, read guides and just practice.
