Don't know about best, but this one just came to mind when I saw the topic.
I'm playing Halo 3:ODST on Legendary, and I was just thinking about how different it was playing as the ODST Rookie, as opposed to the Master Chief in Halo 1-3 who, let's face it, was an 8 foot tall cyborg, this guy was less a man, and more a monster truck who just happened to walk like a man. This was a pretty powerful dude.
The Rookie on the other hand you spend most of his levels, completely alone, with not a whole lot of firepower, and esp on legendary, just trying not to die.
So I did a ton of sneaking around, and I got my hands on a Mongoose ATV. Thought maybe that could give me a bit of an edge with the Brutes the next time I had one I didn't want to fight straight up. So I get cornered, line it up, and go head on one with one. Likely if it had been ANY other difficulty, I'd have pancaked the bastard, I mean I had him dead to rights.
But, this was on Legendary.
So the Brute ran THROUGH me and the Mongoose, and I wound up with my spine wrapped around a very inconveniently placed lamppost.
Never even saw which way was up before he came back around and killed me for good.
Brutal and borderline painful to watch? Absolutely.
And it was awesome.