I have models from Bburago, Maisto, UT and Autoart and Auotart's quality and detail is far and away the best, and their model's are deservedly more expensive.
For instance, the Gran Turismo BNR34 that has been mentioned in this thread from Autoart has Brembo brakes with tiny Brembo insignia, the engine bay is accurately coloured with several paints, the vented bonnet has genuine vent-slots, the glass in the doors (though plastic) is completely frameless as in the real Skyline, there are tiny seat belt buckles front AND back (made from some chromed plastic and then with plastic seat belt threaded through) and the interior (including the boot) is fully carpeted. Awesome.
On top of that you get the full opening/shutting boot/bonnet/doors, tiny pedals and working steering on just about every other 1:18 scale model car.
I would say, however, that paint is not always perfect (though certainly better quality than other companies' models) and if you can have a look for any defects if that worries you.
From the perspective of a model as something to see everyday and appreciate, the greatest factor for me in choosing Autoart would be the fantastic detail, in particular the fact that all the parts are wel-machined and fit together perfectly so that all shut-lines (between body and doors, bonnet, boot etc) are really quite small and don't disrupt the car's shape.
Companies like Autoart also have the advantage of making some really cool cars that other companies don't bother with (or don't have a licence for?) such as racecars, older cars, more familiar/everyday cars, Japanese cars etc.
BTW. Does anyone know what companies make 1:18 scale models of the Ferrari Enzo? At the Sydney motorshow, the Ferrari stand was selling these models, but made by HotWheels (which is not a brand I am particularly familair with when it comes to this sort of model). Is this exlcusive?