Why Hitler in particular? Surely there are other, more generic, people we could use as an example. And if you really want to use Hitler as an example, what makes you think that Hitler was worse than a serial killer, like Jack the Ripper? Both of them killed, but Hitler's murders were indirect, and after a short while they just became a number. Of course, that does not even begin to say that he did not do anything wrong, but is Hitler a worse person because he killed more people? 6 million (the number of Jews he helped send to their deaths) is a big number, and 11 million (the estimated total number of people he murdered) is even larger, but that's all it is. A number.
That said, I personally believe that nobody deserves to suffer for eternity. In my "ideal" vision of hell, mankind's desire for wrongdoing is purged from him with a suitable, ironic punishment, leaving him a polished and reformed future citizen of heaven. So perhaps an ideal "hell" for Hitler, since you mentioned him, would be torture by numbers, and he'd always see numbers escalating, escalating, escalating, until he couldn't stand it. Then the numbers would fade, and after a brief reprieve, they would return only to escalate again. He could hear the whispers of those he killed, their sobs and screams, and feel the cold steel of a pistol against his skin, but pulling the trigger on himself would only cause pain, not distraction....
I'll stop now. Though I don't believe in it, the concept of hell really interests me, and sometimes I get too creative for my own good.

I actually like the way you think. IMO punishing people after death is pretty pointless.
I chose Hitler because he's just the most famous person who has killed a lot of people. I agree there are some killers who are qualitively worse (such as Ted Bundy) and even a few who are quantitively worse (Stalin).