I believe that standard "spade tip" forceps which are often used by stamp collectors are best ! They are extremely thin and "gingerly" grasp the costal vein of a butterflies forewing. They can be purchased at stamp/coin shops and even "hobby lobby" stores. I have never seen or used these but, it seems the coating may be apt to have scales stick to it or otherwise be rubbed off by them. The forceps which I mentioned tend to be chromed with a thin finish so they are not just bare metal. Therefore there is little or no friction present. Yes, there are many small, fine caveats to this hobby you won"t learn from a book or the internet !
I also use stamp collectors' forceps, although mine have a rounded tip. I'd avoid one with a tip that's more pointed than rounded, as it would be easy to puncture a wing. I've used the same pair for decades! I'd avoid a rubber-tipped pair; it seems to me that it would be "sticky" and apt to remove scales.
Olivier, I've tried multiple times to use a setting pin, and I truly cannot do it! All of my specimens would be filled with holes if I kept trying. Only forceps work for me...they'll remove few if any scales if done properly.
I also use the same forceps, round tips, flat for stemp collectors. The coated one with rubber besides will most likely remove more scales will not glide smoothly on the board surface. Entomological pins don’t work for me either. Always ended up with hole. I was only successful with very fresh specimens. Sometimes I use pins for very small moths or Lycaenidae where tips of forceps are covering whole wing.
I have always seem spreading videos and people use forceps or pins to hook a vein and pull the wings up without putting a hole in the wing. It seems quite easy with a large butterfly that is fresh, but I don't see how it is possible to do the same with a small butterfly or moth without making a small hole. The veins simply don't grab well and you can pull up the forewing with a forceps but the hindwing will not be manageable, easy to tear, or will pop out. So I'd be holding the pin at a sharp angle forward to prevent it popping up and drag the wing up by making a tiny hole, and then removing the pin and placing the tracing paper over the wing to hold it in place.
Then there are the skippers that want to stay folded up no matter what and you almost need to make holes to keep the darn wings close to flat so you can make the adjustments and then place the setting paper and remove the wing pins when the specimen is fixed. The methods in books where they have the paper over the specimen WHILE setting seems awfully cumbersome for a small moth or a skipper, especially if you are trying the access the hindwings without putting holes and manage to keep them where you want them.
I only ask because I have always set with 000 pins through each wing and then removing when the spreading paper is in place. I didn't think this was a bad thing but I see a couple people above rolling their eyes at tiny wing holes like it is a rookie mistake.