Jings Deafnala, I might've found someone who hates more dragon minis than I do.

I'm pretty obsessive about dragon minis (that guy talking about the history of the Millenium Falcon is lucid in comparison) and most, IMO, range from 'nice details but rubbish anatomy' to 'sculptor isn't entirely sure what putty/clay is yet'. And no, I've never met a dragon in the street either; but I think at least a very basic grasp of animal anatomy and weight/posing is beneficial when you start to design the thing.

That said, I don't think I can single out a favourite dragon mini. It's easier to narrow down my favourite dragon sculptors.
So going way back to the mid-eighties, there's Julie Guthrie and John Dennett, who sculpted a fair few dragons for Grenadier. Both had a
great grasp of anatomy and posing, IMO. I don't have any nostalgia for their output - the minis were released years before I got into wargaming (a couple of years after I was born, even) - they're just that informed, and intuitive, and
good.
Julie had her name put on a few Grenadier lines, but her
dragon line is the relevant one here. The blue dragon, minus wings, is a pretty good Allosaurus that still holds up after the palaeoart shifts of the 21st century. That's a good credential in my book! I also like the weight, the flow of the lines, and the fine textures in her green, red, and treasure dragons too.
Happy to note that she returned to dragon sculpting in recent years, for Reaper, and she only seems to have gained talent. The pathfinder red dragon and temple dragon that Affun posted are two of hers.
John sculpted half the dragons for Grenadier's
Dragon of the Month series 1, all of the dragons for series 2, and a
few more besides.
Granted, some of his series 1 dragons seem a bit basic, but I still think there's some great naturalism in the stretch'n'squash of the muscles of their limbs, and the way their claws clutch the bases. I think he hit his stride in series 2, which has some real gems. The shire dragon that ThrowsFireball posted is one. The sea dragon coils and flexes in a very realistic way, IMO, like a real snake or eel, and the scale texture is ridiculously fine. The chaos dragon is one I ordered from Mirliton, through Vexillia, and I didn't realise how fine the detail was in
that 'til I had it in my hands. All the wrinkled, dead skin stretched over limbs and the skull, and all the rest. I hope Dirk Stiller doesn't mind me hotlinking one pic from his gallery, but his fantastic painting really shows off the quality of the swamp dragon sculpt:

Rest of his pics are here. Go look!
http://www.theminiaturegallery.deBut the one dragon from series 2 that I make goo-goo eyes at is the dragonlisk.
http://www.minitaly.com/paolo/It's got that inscrutable reptilian sneer in it's eyes and mouth, atop a twisty, wattly, neck. It's got stringy little muscles and tendons in it's legs, under wrinkled skin, wrapped around it's drooping belly. It's wings are a bizarre mashup of featherless bird and pterosaur. It's an ugly little spud, and I love it because it's designed and put together
so well as an ugly little spud. As opposed to a mini being ugly because the sculpting is a bit...
inexpert. Getting one of these on ebay has to be one of the highlights of my hobby. John Dennett really got it.
(Okay, the polo mint scales are a bit funky, but given another of my sculpting pet peeves is lots of nice detail to hide bad structure, I can well live with this inversion of that!)
As far as I'm concerned, the gaming-mini dragon situation was a bit lacklustre from then, 'til more recent years; with one notable exception of Sandra Garrity at Reaper. Among later releases, I like the Confrontation dragons; well-built and with a bit of imagination in the design. I think I prefer the sense of weight in the the smaller, four-limbed dragon of Lanever. I also have to nod in appreciation at the Warploque and Oathsworn dragons, too. And as said, Julie Guthrie at Reaper.
And special mention to the Heresy dragon. Aside from the fact that it nearly bankrupted and killed him (in either order), and taking it on it's own merits, it's a great piece of work. It's got a good balance of pose, structure and detailing. Another high point of my collection.
To be honest, Tom Meier and Nick Bibby dragons don't spark too much with me. Nick in particular: while the stuff
he sculpts these days makes me want to weep from the sheer beauty of it and because I'll never,
never be that good, I find a lot of his old wargaming dragons a bit lumpy or oddly stretched into pose. (I mean,
eh? Whut?) And Trish Morrison/Carden seems to have picked up his old tics and run with them at GW for a couple of decades. Overall, I think my favourite of his, more than the great spined dragon even, is the
dragonmasters dragon. (Maybe with a little orthodonty)
Of course, there's something new that might just edge it out...
http://nickbibby.com/?product=firedrake-dragon