Just how hard is it to kill a Troll?

[Eomer of the Rohirrim]

Trolls. 'Created' by the Dark Lord in mockery of Ents. Right? So why am I just now realising that they must be pretty big, indeed way bigger than Orcs. I feel like an idiot!

Anyway, I watched the Fellowship movie the other night and this new thought came into my head. So the Cave Troll perhaps wasn't as exaggerated as I had previously thought. Well, maybe a bit.

I thought about it some more and said to myself, " Hey, the Fellowship actually did pretty well to kill that beast. Good on you."

Then I considered Hurin. Hurin the Elf-friend, who at the Nirnaeth Arnoediad killed at least 70 Trolls single-handedly. I also remembered reading a post on another thread telling me that Ecthelion had killed over 100 Trolls in one go.

How big were these Trolls? How was Hurin's tally so immense? Just how hard is it to kill a Troll?