Here's a question, does it really have to be a laptop? Personally, I'd be looking for a used HP Z series workstation. Media companies surplus them out by the pallet-full. What was an $8,000 computer 7 years ago is a $300 computer today, and still a pretty great computer.
Or, pick up anything 2nd-gen i5 or newer, stick 8GB or more RAM in there and a cheap FirePro card and you're good.
If you must go with a laptop, personally I would never go for used or refurb on a laptop unless it was dirt cheap. Also on laptops, I would choose a Full HD (1920x1080) or better screen first over any other characteristics.
For new,
this is about the best deal currently for something with dedicated graphics.
Without dedicated graphics,
this.
If you want an SSD,
this.
If you're running Solidworks, I'd probably recommend going for the dedicated graphics. If you're running Inventor, you'd be surprised with how good Intel graphics can be.
Attached is my full laptop selection guide, because this is not the first time I've come across this question.