Worst? I have to strongly consider the Exorcist and Wood Elf Dragon Sisters of Twilight kit. Everything seemed to be going just fine (I had a pre-release it with a piece of the base missing, so I had to sub in one from my own bitz box) until I had to glue the head on. Turns out the body was slightly twisted or something because the head wasn\'t going to go on straight at all. So lots of careful twisting and bending hoping I wouldn\'t snap off any of the double pinned joints...
In the end I magnetted the head on for ease of painting and also if I ever want to use a non-special character Dragon in the army I can just bitz order another head and use some more of my uber magnets.
The Exorcist went okay for the most part, surprisingly well for a GW kit with big fat metal pieces on it. Everything went well at first (again) until I assembled the little turret thing with the SOB playing the piano keys. One of the sides of the turret thing was INCREDIBLY poorly fitted, it was about 6mm thick and the pieces were supposed to interlock like a jigsaw puzzle. They weren\'t even close, it took a TON of grinding/filing to get the two to fit together, and then I had to greenstuff over the area to hide the mess. Took ages even with a Dremel because the metal was so damn thick.
Another supremely annoying model for me was the standard Commander Sorscha figure. The top and bottom of the hammer have broken off a number of times already on the model, and all I\'ve painted so far is the base. And it might be too thin to pin. I\'ve pretty much resigned myself to buying the alt pose at some point so I don\'t have to deal with it anymore.
My biggest shock ever with big metal models was the Master of the Ravenwing though. The one I got a few weeks ago had almost no flash/mould lines anywhere on it, and has no twisting, warping, or anything like that.
The phrase \"Like a glove!\" comes to mind.