I've used a lot of Bosch being a VW guy. But I've had problems with them in lots of cars - including Volvo's. It seems the more exotic (multiple tips, rare metals) the more issues on a variety of cars.
I use the NGK Vgroove's with the green printing on all the Suby's that I do. Around 2 bucks each even at the big chain stores.
I have seen and removed well used Autolite plugs out of 2.2's and you certainly can't get any cheaper than them.
I only use Champions in lawn mowers. I used to be able to tell on an air cooled VW if it had ever had Champions in it. I think their thread pitch was a little off for that application.
I've even started putting NGK's in VW 2.0's with great success.
NGK is OEM for a lot of the GM Saturns.
I have used some Nippon/Denso's but not enough to have an opinion.
Price, performance, and not being finicky NGK's are shaping up to be my favorite plug. And the price isn't bad at all. Even the "laser platinums" the GF's 2006 Impreza takes really aren't that bad cost wise - IIR under 8 bucks. I think their interval had to do with no anti-seize from the factory more than wear. They looked fine when removed.
BTW - this has all the potential of becoming like an oil brand thread. It'll be interesteing to see where it goes. My observations above were from real world experience, we'll have to see who's experience's differ and what the scientists have to say.
Edited by davebugs, 02 April 2009 - 07:37 AM.