What, in your opinion, are some of the troop or hero choices available that have the highest Risk to Reward Ratio? ie, if they go wrong then they go WRONG but if they go well they go really well?
Anyone can spam Moria goblins, and there's not much you can do wrong with them, but there are obviously choices out there that are more difficult to use, and yet more effective. Anything with a glaring strength but a gaping weakness, really.
All hero armies are difficult to use, but under the right circumstance can wipe out other players.
What would you think?

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Taking Smaug to a game. You risk damaging that model in so many ways, but as long as it works out, it looks glorious (and eats anything it comes across).

On a more serious note, a good example would be Gûlavhar. Very expensive, but can rip through most stuff with quite some ease. Once he gets wounded, however, his power diminishes significantly, making him even more vulnerable, which in turns makes him even less powerful.

Wood Elves, more specifically Mirkwood Rangers or the old Sentinels also fall in this category. They're good at winning fights, but every time they fail, they'll drop as quickly as a 3pt Hobbit. Even the mighty Thranduil, although having a >80% chance of winning the fight when surrounded (not even taking into account Might points), killing a few of his assailants each turn, will at some point not roll high enough and can suddenly go down. You want him against a good few opponents to get all those extra attacks, but then risk taking a few painful hits if failing to roll that 6 to win.

Yeah, Gulahvar is very difficult to keep alive long enough to start chewing through troops, but once he gets going you better hope you've got a hero to stop him. Very specialist piece.

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