My go-to brand is NGK. They make the best spark plugs
Denso is also good, and often at a better price than NGK. So they are a close second.
If the plugs are hard to get to, like most transverse V6 engines, iridium is a MUST! That way, you won't have to do it again for a long time
If the job is easy, I just stick to OE-spec plug, provided they are still easy to obtain at a good price. Otherwise, NGK or Denso. One example of this is the 00-04 Volvo S40/V40, which originally called for a Champion (platinum) RC8PYP, which they don't appear to make anymore. In that case, I'd go for NGK platinum (or possibly Champion iridium).
For cars that have spark plug wires, I like NGK because of the cool blue color, and because they are numbered for easy identification.
One more exception is the mid-00's Ford 3V 5.4L V8 with those stupid 2-piece spark plugs. For that engine, I'd use the iridium plugs Bosch just came out with. They are finally on sale now. Autozone has them for $8.99, but online-only. Free shipping, no minimum, plus 20% off with an online code, AND a $3 per plug rebate! The Bosch Iridiums are made in Germany. Part number 96322.