Your question is fine if you just want to know what plug someone is running, BUT if you want to know what is recommended for your build and use, a lot of additional information is needed.
Since I have gone through 1000's of plugs personally, and in customer cars, I do have preferences based upon results we have found for street, strip and in-between.
My first comment is that I gave up on AC Delco spark plugs years ago when we found many of them were defective and would cause many weird issues?
Our plug brand of choice is now Autolite for 2 main reasons, they have excellent quality control in their entire product line, and we are extremely familiar with how they perform in all the application that we have used from street use to 7 sec. track cars. Also, availability is easy and affordable, as companies like Summit carry a full line of Autolite plugs.
To determine a spark plug "starting point", it is very important to know on how the car is being driven/used, type of head alum or iron, and other factors in the build like fuel, pump or race gas, alky injection, E-85, HP level, RPM range and data on the hardware in the build.
Even if you know all the given info on a particular build, it is still necessary to know at least the basics of reading your own plugs to determine if they are the optimum heat range for you. Lots of info on-line how to do this.
It is always best to start with a colder plug to prevent any possible engine damage when experimenting when performance and HP has been increased. If it would cost you a set on plugs vs. a head gasket you can see why this is a good method to start cold, then move up to a hotter plug if needed.
With alky injection, E-85 and race gas, you must be very careful in plug selection as the increased HP/cylinder pressure can easily and quickly cause a hot spot which is almost always the spark plug tip? This is also the reason NOT to use a projected tip plug with these applications.
As far a "designer" and speciality plugs, leave them to the people with the feeling that more expensive is better, at least for their ego, not so much for their turbo Buick!