the hellcannon crew. but if your talking about big hats, then I'll have to go with astragoth as well
I like the plastic Big Hat Warriors. They simply supreme ranked up in one giant unit.
Either the Hellcannon crew, If we dont count them, then some of the old Hobs.
As for me - the truely greatest CDs are to be found in the old 3ed/Marauder-line. And a favorite would be Doomaxe from the Renegades (Though it's a close race against fine models as Khazek, the Master and the Mage).
If it has to be a Big Hat I will go for "
Hero with axe 1"
Hero with axe 1 very cool figure even though it lacks dynamism

Oh mustnt forget the Marauders all are great
I'm going to say Sneaky Gitz as well, very characterfull models

.
The axe is a little too big but other than that, it's very dynamic. There's worse 3rd Edition Chaos Dwarfs than Foaming Mad, trust me.
waslooking throgh the old catalogue yesterday, i have to say the swivel gun crew are pretty cool
Oh! yes Pyro - totally forgot about him:
Took the liberty to rotate him for better enjoyment.
He is defently the greatest big hat.
Pulper Spikehead!
Also the Marauder miniatures deserve an honourable mention...

Any of the figures from the 3rd edition days would get my vote.
I would of saif Hero with Axe 1 but his shoulder pad with the skull on the end of the spiky bit looks a bit weid to me.
What the hell is that spike about!?
Pose is great, hat is cool, weapon could be better (as could every weapon in the big-hat range!), but that shoulder thing is just wierd!
The big-hat drummer is an awesome model!! it doesn't look much in pics, you only realise how cool it is when you get it. I found it the same with the Hobgoblin miniatures.
what was i thinking...I'm changing my answer. Marauder CD's all the way!
As for me - the truely greatest CDs are to be found in the old 3ed/Marauder-line.
Quoted for truth.
Although it's not the best sculpted CD i've ever seen, i've always had a soft spot for the CD zombie Ninja (mostly because it reminds me of a time when GW had a sense of humour).
And for non-GW CDs, the Heresy Dwarf Vad'urr miniature.
The Khazek model is quite cool. I think I have him lying about somewhere.
- Tallhat
Then there is no excuse - not to dig him out, dip him with some paint and post some pic. - is there
Oho. Might have a look there

Thanks Cornixt.
It took me long enough to make, so someone should use it! 
I'm pretty sure I've covered everything, but if there are any ommissions it would be nice to know.