Crazy Modeller vs. KA Models vs. Hobby Design?

I'm mostly an aircraft modeller, but I've been getting into cars lately. I have a bunch of kits that I'd like to add some PE to, but I'm not really up on what's good and bad in the auto modelling aftermarket.

There's a fair bit of duplication between the subjects covered by KA, Crazy Modeller and Hobby Design, so who has the better etch? Are any of them to be avoided?

Welcome to AF.
All the brands listed are good. If you are looking for a set for one specific kit, one brands product may be more complete than another. One company may offer a small set for a specific kit while another may offer a set including lots of parts. If you just want to add some badges than a foil transfer set may be the best bet. I guess what i'm trying to say is the best set depends on what you want to do with it.

I'd second that. It really depends on what model kit you have and how extensive of a PE set you want. Hobby Design and Crazy Modeler tend to have the overboard PE kits that include everything under the sun (and most you probably won't use). Both HD and CM usually have some kind of 'basic' kit though that includes the bare minimum like Studio 27 or Tamiya's PE upgrade sets. KA models usually has some one-off PE sets (like the Toyota Harrier SUV for instance).

I personally have been buying some HD sets lately mainly because they're the only ones available at the time for the kit I have or it has certain parts I'm looking for.

Again, depending on what you have there is also Scale Motorsports and many other companies available.

You'll probably get at least a handful of responses saying PE is overrated and a waste of time but I personally like some PE here and there.

PE is overrated and a waste of time.....(No, just kidding.)

But there has been an explosion, it seems, of aftermarket PE producers and their offerings. Often there are multiple frets available for the popular kits. I've noticed that the frets are getting much bigger too. But when I look at these bigger, more expensive PE frets sometimes I see some slight-of-hand taking place. Take, for example, the Crazy Modeler fret for the Fujimi Ferrari 288GTO. It's much bigger than the Studio 27 piece and more expensive. But looking closely at the fret I see: 6 license plates, 2 giant specification plates, 6 poor looking 2-D seat belt parts, 8 rotor surfaces (which make the rotors too thick) and various odds and ends that might look good if they were a little smaller. Most of the fret that is left is for vents in the bodywork. The fujimi 288 body vents look very good and replacing them would be major surgery. And after all that, would they even look better?

My only point with this post is to suggest that you look closely at each part on a fret and mentally place the part on the model before deciding if it's worth buying. I didn't mention fit accuracy here so maybe someone else could address that one.